When you first launch up garry's mod, you are introduced to a screen with moving backgrounds. Before you start, check your options to see if everything is configured to your liking. When you are done with that, starting or finding a game is simple. I would recommend to hit start new game and start a single player server to familiarize yourself to the game.

Now if you noticed, you have a physgun and toolgun, these are both very helpful tools. Lets start by learning how to use these. First, hold down Q or whatever you binded spawn menu to, and you will be greeted by a big interface. If you look to the right, you will see a small tab with 3 labels. Tools, Utilites, and Options. Tools is for your toolgun, the most important tools for building is, weld tool, rope tool, thrusters, no collide, hoverballs and wheels. If you want to make things like elevators, look around in the constraints. If you have spawned a prop, you hold the prop and hit right click to freeze it. If you hold c, and click on the prop, it opens up a context menu with options that can be fun to mess around with or helpful to you. Now, with the prop you have, to unfreeze it, simply grab it, or hold it and hit R. If its a ragdoll, grab the body part you froze, or hold the ragdoll and hit R. Now lets say you want to rotate the prop, just hold the prop and rotate it by holding e or whatever your pickup button is. If you want to put it a specific angle, hold shift and e or whatever your pickup controls is binded to. Now, you may be tired of walking around, its time to fly. First, hit V to noclip, or you may have it binded to another button. Next, you can hold shift to go faster, you can hold alt to go slower. You can also go through walls or any structure with noclip. Lets move on now.

So, you want to meet new people now, yes? After you have disconnected from your singleplayer server, its time to hit find multiplayer game. Now before you go off and try to start every other gamemode, I would really recommend starting off in sandbox, on servers like NFO, or ones simply titled Garry's mod. If you really want to try other gamemodes, remember that some servers need certain content, like CSS or TF2 or L4D2. This means you will have to buy those games and mount them onto gmod. Let your mind run wild in sandbox, or find a pvp server. This game is endless opportunities.

If you have had enough of sandbox and want to move on, then lets look at some other gamemodes. If you are looking for something serious and comedic at the same time, try TTT for example. The community all depends on the server you play on. If you want to have a serious but fun server, try serious TTT. If you want servers that are fun and secured by top anti cheats, try MOAT. Say you want a fun gamemode thats also a bit competitive, try Zombie Survival. Be aware, this gamemode requires css. If you want something very toxic and serious, try darkrp. I personally cannot recommend any other gamemodes as I do not play them very often, so look around and let your mind run wild.

Finding your singleplayer servers boring? Need more stuff to mess around with? Check out the workshop. If your in game, just hit SHIFT+TAB and then hit workshop on the top right. Whatever category you want, just click the box that says (none specified) and hit whatever tab you want. The workshop has a lot of great addons. Be aware, certain addons require certain game content.

You found out, that many addons and gamemodes require game content. I would recommend starting off by getting css, as that is the one that will most frequently pop up for requirements on servers. After that, get whatever else games you need, but I would also get hl2, hl2 episode 2, and hl2 episode 1. If you want to mount the content onto the game, in the main menu, hit the controller button at the bottom right, and click the games that you have just bought and download.