This is the GBombs 5 addon that I used,
I am also the original creator of all images used in this guide, but all credit of making the addon goes to the original creator of GBombs 5, and the person that reuploaded it without the backdoors.

Alternatively, you can also use this pack https://gtm.steamproxy.vip/workshop/filedetails/?id=951835995

Many people have problems with artillery, as they don't know how to actually use it.
First off we will talk about the launchers, and the ammo used in them.
Howitzer

• Howitzer Chlorine Shell, a shell, that when exploded causes a gas to form around where it was detonated, which distrorts your vision and makes you slowly lose health, the Gas Mask in Protection makes you immune to the effect.
  
• Howitzer Frag Shell, a shell that when exploded launches several burning fragments in all directions.
  
• Howitzer HE Shell, a High Explosive shell, a normal shell, it hits something and explodes.
  
• Howitzer Incen Shell, a shell that you can (in-game) compare to Napalm, when it explodes, everything around it will start to burn, and this is a different kind of "burn", not the normal gmod one, as it does more damage and you will continue to burn after dying.

Now, how to use the Howitzer? There are two general ways, either put the shell in the back of the barrel, or in the front, near the front for slightly longer range, and near the back for more precision, but in the end it doesn't really matter.
So, put the shell of your choosing into the barrel, then put the Howitzer Propellant behind it, arm the shell using E, make sure it's unfrozen, and then press E on the propellant.
This pretty much applies to all artillery.

Atomic Annie, you don't really need the base, the barrel is the important part.
The only shell for it is the Mk33, which is a nuclear shell, do what you did with the Howitzer, and you will be fine, if you are lucky, because sometimes it blows up at your end for NO APPARENT REASON.

Davy Crockett, this is also a nuclear shell, the loading and firing is a little bit different here than with the other 2.
First put the Davy Crockett into the front, and put the propellant inside, near the shell, make sure to arm and unfreeze the shell, and then press E on the propellant to launch it.

Now, sometimes you don't want to mess around with launchers and propellants, I got some fantastic news for you, the Tank Shells, come in 3 sizes, 135mm, 170mm and 240mm.
They dont need propellant, or a launcher, you just aim, and press E to launch them.

Chemicals, the worst and least humane part, but one of the most fun ones as well.
First off, the Mark 77 Napalm, used in Vietnam, that caused a lot of deaths, and basically can set anything on fire.
In GMod too, buildings, the ground, NPCs, Players and props, you name it, it can set it on fire.
This is a very nasty fire and stays for a long time, same as with the Incen shell, but on a bigger scale.

Poison Gas, a gas that slowly blinds you, and makes you unable to move, I don't actually know if it does damage, but it does limit movement, and blinds the person.

Now, VX Gas, a gas that makes you a ragdoll and throws you around, this doesn't cause any damage, but is still pretty bad.

Lastly, the T-Virus, and the cure for it.
The T-Virus is a nasty one, infection can range from dropping the virus nearby, to standing next to an infected person/zombie, or getting clawed by a zombie.
This can be combatted with the Gas Mask and the HAZMAT Suit in Protection.
Though, even if you have HAZMAT or the Gas Mask, if a zombie hits you, you will still get infected.
If you have a big problem, in a city or some other place, and a lot of people, a common and good tactic to limit is to create a safezone, and quarantine new people that come to test for infection, and immidiently kill or isolate infected people, then after some time, kill off the remaining zombies.
The killing of zombies is when Napalm is actually pretty useful, you can use Napalm to quickly take the zombies, and the infection out.

kotomtom02 gave some vital information about this. Thank you!

Smaller nukes only need uranium, but as you get bigger and bigger, you need plutonium.
If you have too much uranium or a bad mix of uranium and plutonium, the nuke will not explode. You need to test and balance it so it works.
Tritium also plays a role in bigger nukes and has a similar effect to plutonium. Bigger nukes need a lot of knowledge and experience to be built properly
You put all the parts near each other and then activate a nuclear initiator.
With this you can make your own nuclear bombs, make your own shell out of props, put some Uranium and an initiator inside, and there you go.

Now we get to the juicy part, bombs!
The Light Bombs are bombs that have less than 200 lb(pounds)

The first bomb in the list is the Breaching Charge, this is a small explosive sometimes used by military or police, that can blow up walls and doors, in GMod, it can destroy doors, even locked ones, so that you can come in with a blast.

Next we have the C4, a small bomb used to blow stuff up.

Now the LEB 50lb and the LEB 100lb
These are normal bombs, they go boom when you shoot them, pretty normal stuff.

Now, Nitroglycerin, this is a nasty one, if it falls from even a small height, it will explode.

Then we have the Pressure-Cooker, when you press E on it, pressure will slowly generate inside, and when it gets too much, it explodes.

Then the Schrapnel Bomb, a grenade pretty much, that you can throw, and when it hits something it will act like a frag grenade.
This is pretty much a homemade grenade.

This is a small category, and only has 3 bombs, it's pretty self explenatory, so I won't go into it, but have a picture anyways.

(I could not provide a picture, as many of the bombs models were glitched for me)
Now, these ones have some different properties, so I will go into atleast SOME detail.

CBU-52U, this is a "Clusterbomb" as, when it explodes it launches a lot of smaller bombs in all directions, which then explode, this bomb is good at taking out some infantry squads, when normal bombs don't have a good chance to hit.


GXM11, this is a bomb that is good at destroying everything around it, and even a lot of stuff above it, it makes a big cloud, and launches several fragments upwords, you can use this to take out aerial vehicles for example, or take people out on high platforms.


The Jdam is a pretty normal bomb, with a large radius, that explodes in a "line"


Oh boy, now the Liquid Tiberium Bomb, a bomb from Command & Conquer, it has a green cloud, and not a grayish one, but other than that it's a normal bomb
[Corrected by TheHopelessThrumbo] The bomb also leaves Green Tiberium Crystals after exploding, these are highly radioactive and can kill you in seconds.
These crystals can be removed by any damage source but explode and deal damage.


Now the T-12 Cloudmaker, my favourite bomb out of the entire pack, it has a pretty large radius aswell, and looking at the explosion, you can see why it's called the "Cloudmaker"


Lastly the 1000lb, this is a pretty nice bomb as well.

First we have the LEM - Cluster Mine, when you activate it it becomes invisible(is in the ground), so it's perfect to lay in a minefield, where you know enemy troops will come through.
When you stand on it, it will explode, and launch some white balls, and then those balls will also explode.

Then the LEM - Field Raper, this guy is not invisible, but very effective, when you stand on it, it will explode, and launch tons of explosives, which will later also explode.
There is also the (WARNING OP) one, this one is just a better version of the last one.

Then the LEM - Schrapnel Mine, this mine goes invisible, and simply launches schrapnel when exploded.

I will put these in one category, as there is not a lot of them, and I don't have to get into a lot of detail.

First off, Misc, Nuclear Testing Towers are towers where you can put nukes on to test them, what they are going to do when detonated in the air.
Then the Propane Canister, something that explodes, and the WildFire, is a green fire, that apeared in Game of Thrones.

Then the Protection.
The Forcefield makes it so bombs do less damage when you are in the forcefield.

The Gas Mask and the HAZMAT Suit protect you from airborne stuff, gasses, and radiation.

Sirens, these are cool sirens that you can use to alert people of an air raid, nuclear bombing, or other stuff, whatever floats your boat.

In the Vehicles we only have the fridge from Indiana Jones, you can enter it and... I don't really know.

A lot of the Missile models either didn't fit in the image, or the models were glitched, so sorry for no picture.

First off, the propellants, you can use these to propel something, don't really know what, I never use them. They come in five sizes and get faster and faster each time.


Then we have the Tomahawk missle, some of you may know it from Call Of Duty, or from cool videos of cool soldiers shooting cool missles from cool ships.
Either way, it's a missle that is supposed to be fired horizontaly, not vertically.

the ICBMs go hand in hand, these are Inter-Continental Balistic Missles, and come in 3 Marks in GBombs 5, they pack a punch, and can fly for a long time.

then the V-2, my favourite missle.
This missle is just fun to play with, and the explosion is around the size of a medium bomb.

Now, the most popular part of GBombs 5, the nukes.
I had to move over to Bigcity Improved for this one.

First off, the Antimatter Canister, this one does some stuff as you see in the picture.


Then we have the Cluster-F***ing Nuke, don't EVER detonate this one, your pc will thank you for it.

The Fat Man, and Little Boy, two nukes dropped on Hiroshima and Nagasaki, this is how the look in GMod.



Then the Gadget is the first nuclear bomb created by the U.S. In the Trinity Project.


The Ivy Mike was (to my knowledge) the first hydrogen bomb ever tested.


The Tsar Bomba is the worlds current (known) largest nuclear bomb.

Now, oh boy, one of the biggest parts.

These are bombs that don't really fit in with any other categories, and they do some unrealistic stuff, just for fun I guess.

Anti-Gravity Bomb, this bomb makes all gravity reversed in the nearby area, making things fly up.

Attraction Bomb, and Repulsion Bomb, these go hand in hand, as they either push things or pull things.

Dark-Matter Bomb and Red-Matter Bomb, I believe this is from Star Trek, and basically causes a black hole, or a thing that sucks you in.

The EMP Device is pretty interesting, if you explode it, all electronics will get fried, combine choppers, manhacks, turrets, rollermines, all that.

the Endothermic and Exothermic bombs, are just cool looking bombs, that do cool stuff, I will let you see for yourself.

The Flashbang is... A Flashbang.

The Fusion Bomb does a cool purple explosion, but other than that, it's a normal bomb.

The Hypersonic and Supersonic bombs are bombs that are VERY loud, so turn down your speakers when using them, and they basically launch everything in the air.

The Photon Torpedo is also from Star Trek, and is basically a missle, that isn't affected by gravity, and has a pretty big explosion.
Make sure the "Engine Cool" part is on your side.

Now, the Singularity Bomb is a bomb that will push and pull objects, and just continue to do that for some time.

The Space Nuke is an awesome bomb, with a very nice looking explosion.

• If you put the Endothermic Bomb and the Exothermic Bomb next to eachother, and they explode at the same time, you will get a very pretty explosion.
  
• If you drop the T-Virus Cure next to a zombified NPC (has to be from the T-Virus) you can bring them back!
  
• In order to detonate a bomb remotely, get wiremod, spawn a button with the off value 0, and the on value 1, and then wire the "detonate" in the bomb to the button, activate the button and you will activate it remotely.
  
• If you want to guide a missile somewhere, rope the tip of it to the halfway point between it and the target you wish to hit. It's not very precise but it gets the job done, sometimes. (Added as of May 6th)
  
• (Future Tips&Tricks will be added, feel free to correct my guide, and add some Tips&Tricks in the comments, I will put your name along with your Tip/Trick, unless you want to be anonymous, if you do, just say it.)