Dota 2 is an MOBA ( Multiplayer Online Battle Arena ) you choose one Hero and fight with your Team over a Map to destroy the enemy Base. Sounds easy ? It isn’t that much for Beginners. First you have to choose one Lane ( Bottom, Middle or Top ) there are mostly 3 Lanes and all three should be defended. Now wait for the enemy minions and slay them to level first your chars. Try to avoid fights with enemy Players and keep back to base on low health. Dont forget your kill will give the enemy experience Points, to rush and get only killed is a feed ( grant the enemy many level to get stronger ).
You have a shop system on your base and you have to use it to buy items that give you bonus. After the first levels you try to destroy towers and enemys but still play defend rushing brings only something at the end game.
Other MOBA Games you want to try : Heroes of the Storm, League of Legends