1
Fight against bots. When you first start playing, you’ll want to play against bots first. This will help you learn how to play the game and get comfortable with the controls, so that when you play with your friends you won’t be a terrible teammate. Click on "Play Dota" at the bottom right, then choose "Practice With Bots", where you will be able to select the difficulty and team.
Always play against bots first. The strangers you get paired against will not be...welcoming if you suck.
Another way to play against bots is to join a Co-op bot match. With this type of game you will play with strangers or your team (if you become part of a team) against bots.

Fight against friends. When you’ve got a good idea of how to play the game, you can play against and with your friends. Nothing build friendships like killing your friends and insulting their moms. Create a lobby from the play menu and either password protect it to only play with your friends or leave it open to play against a few friends and a few strangers.

3
Fight against strangers. If you enjoy having your playing aptitude, gender, and sexual preference mocked or simply enjoy making strangers look like idiots by thoroughly beating them, play a match or play a team match (if you have a team).
Choose your game mode. Sometimes you might want to change your game mode. This is possible for any matchmaking game, as well as lobby games. Game modes affect how you can choose the heroes that you, your teammates, and the opposing team play with.[1]
“All Pick” is wide open.
“Single Draft” gives players a choice of three heroes based on attribute.
“Captain’s Mode” (the standard format for championship games) allows team captains to choose heroes in turn for their players from a nearly unlimited pool.
“Random Draft” gives players a 22 hero pool to choose from and turns are taken in choosing heroes.
“Least Played” removes your 40 most-played characters from the pool.
“Limited Heroes” is limited to the easiest to play heroes.
“All Random” is pretty much exactly what it sounds like.
Adjust settings. Don’t forget to make sure the settings are correct when you go to join a match. The settings can help get you matched with the right people and make sure your connection is strong, combating rage-inducing lag. Remember: Lag kills. Friends don’t let friends lag.
The most important setting to pay attention to is region or server location. You want to play against people and with people that are close to you if you know your connection is slow. This will help ease lag issues.

1
Choose a character. After joining a match you will choose your hero (or have one chosen for you). What character you choose is really important, so don’t just choose the red-headed chick because she’s hot. That is a bad plan. Choose your character based on how you play best and based on what your team needs. There are many roles[2] but here are a few:
A “Durable” or “Tank” is a hero who purposefully draws the enemy attention and takes damage while the other teammates work on taking out the other team and the towers. Good examples of Tanks are Axe, Dragon Knight, and Elder Titan.
A “Carry” is the hero who will deal the majority of the team’s damage, theoretically ranking in the most kills by the end of the game. At early game, this role is still weak and needs a great care of the supports for they will be carried in late game. This is a powerful role with powerful heroes, but it takes a great deal of skill to pull off. Good examples of Carries are Phantom Lancer, Medusa, and Spectre.
A “Lane Support” sticks with the team’s carry to keep them safe, healing them or replenishing their mana. These heroes generally do not make kills, and accordingly do not get gold. Good Lane Supports include Lich and Dazzle.
A "Support" focuses on buying the courier and buying the wards to give vision to his/her team. Great supports include Crystal Maiden and Omniknight.
A "Initiator" starts the clashes and manipulates the war. They have the abilities that can disrupt the formation of the enemies, leaving them unguarded. Great initiators are Clockwerk and Tidehunter.
”Pushers” are the heroes who focus on bringing down enemy towers as quickly as possible. Examples of Pushers include Broodmother and Leshrac.
If you’re familiar with the role of mages in other games, then you’ll understand the “Nuker”. Nukers deal damage using spells with large areas of effect, often from a distance. These characters make great Pushers and the roles can be doubled.
You can always random if you think you've got what it takes. If you random you'll get 200 extra starting gold. But remember, you can't random in the last 10 seconds of the picking phase, so don't wait too long.

2
Attributes determine the effectiveness of the armor, the amount of health your hero has, and the amount of magical power (or mana) that they can draw from. Each character has a major attribute (one which is higher than the others) which greatly determines how they will play. Attributes increase with level.
Strength, which builds health, is essential for heroes who will need to take a lot of damage.
Agility, which builds defense, is essential for heroes who will carry the team (explained below).
Intelligence, which builds mana, is essential for supporting heroes or those who intend to attack from a distance.

3
When you first enter the map, you will be placed next to the store, where you should buy some items. You can purchase consumables (potions and similar items), items which fortify your attributes, armaments to protect yourself with, and magical items (if your character is so inclined). You can also return to the shop during the match or buy a Courier which will take items back and forth for you.
Use secret shops. There are also secret shops hidden in the jungles between the roadways (or lanes). These sometimes have items for sale which are not available in the regular shop.
You will purchase these item with gold. Gold is earned passively (every few seconds) but also for things like killing enemy soldiers (called Creeps), destroying enemy towers, and various other accomplishments.

4
There will be two runes in the river, between the three lanes. They give short-term boosts and disappear once taken. They respawn every 2 minutes. They can be stored in a bottle (purchased at the shop) to be used later

1
There are three main roadways on the game map. These are called lanes. During the game, you and your enemies will largely be positioned in these lanes, in varying numbers, where you will fight for control in order to reach and destroy each other’s towers. You and your teammates will need to figure out how you want to handle your lanes.
Center Lane - The Center Lane, which go diagonally across the screen from base to base, is usually played with one hero versus one hero. This is why it is often called the solo lane. Players in these lanes will commonly move to the outer lanes to create uneven numbers and gank (or gang kill) the enemy heroes.
Top Lane - The top lane is usually played 2v2.
Bottom Lane - The bottom lane is usually played 2v2.

2
Work together with your teammates to slowly chip away at the enemy. Remember, the goal is not to kill them but to instead destroy their towers. Be strategic and play your hero well. There is no “i” in team but there is an “i” in ♥♥♥♥: support your teammates and together you can all succeed.
Creeps, the funny looking fellows that you can’t control, are also part of your team. Use them. Worship them. They are the key to your success. They will spawn every so often and come in waves down the lanes. There they will clash with enemy creeps and towers, protecting you from much damage. Stay behind the creep line of defense.
Destroy the other team’s creeps to gain money, though. Those guys are jerks.

3
The game is won when the enemy’s main structure, called their Ancient, is destroyed. This main tower is located on the opposite corner of the map from where you begin. Progress your way there by destroying the intervening towers that block your progress.
The other side of this, of course, is that the enemy team will be trying to destroy your towers. Protect your towers.

4
Mostly you’ll be dealing with enemy creeps, sometimes enemy heroes, and hopefully the enemy towers. Attack the enemy but never forget your focus of getting to their towers (and eventually their Ancient). Don’t be stupid and don’t be rash, take your time and make smart kills.
Right click on enemies to perform basic attacks.
Use and advance abilities through the course of the game. Abilities will be different for every character. They are assigned to keys which you choose when you start the game. Experiment with abilities and find the best ways to use them. Make sure you use them to help not only yourself but your team as well.

5
Last hit is a very important aspect of playing DOTA 2. Only the person who gets the last hit on an enemy gets the gold (though all in the immediate area get the experience). If your character is one that benefits from gold, make sure you’re getting the last hit. The best way to do this is to wait until you see an enemy’s health is low and then go in for the kill. Timing this is a learned skill. Don't forget that last-hitting will also push the lanes forwards if not countered with a friendly hit.

6
You don’t want your enemies to get gold or experience for killing your creeps, so when you see the opportunity, kill your own creeps to deny them the pleasure and rewards. This should be done just like last hitting.

7
Don’t forget that there are neutral creeps in the jungles between the lanes who will attack you given opportunity. There is also the dragon Roshan lurking just off the lanes and he will deal out a butt kicking like you can’t even imagine. Be cautious.

8
Pick up some healing salves at the beginning of the game (from the store). These will allow you to regain some health while fighting. Later in the game, after winning a hundred battles, you will be allowed to teleport to base for free (which will also heal you).
Heal yourself by returning to base. You’ll need scrolls to return to your base, so this isn’t ideal, but it’s preferable to dying so keep it in mind.
You can also use tangos. A tango is an item you purchase in the store at the beginning of the game. Use it in order to gain back some health. Using a tango allows you to cut down three trees which are then converted to health.

9
Remember, this is a strategy game. A STRATEGY GAME. Not run-in-and-kill-things game. It requires skill and patience. Dying is seriously punished, so you will need to play smart. Dying means you’re missing out on experience and gold, and your teammates are going to get gut-punched while they wait for you. So, yeah, don’t die.