LoL is based on the well known "DoTa" map of Warcraft III and was also developed by the creators of DoTa Allstars.
The game consists of ~60 champions which you can use to be successful on 2 differnet maps:
|3on3 map 5on5 map|
The game principle is explained easily but it takes time to know how to play well.
The goal of every match is to defeat the opponents team by rushing into their base and destroy their nexus (the last building). But to get there you first have to destroy the towers of minimum one of the lanes (there are 3 lanes on the 5on5 map and 2 lanes on the 3on3 map) and minimum 1 inhibitor (those are the buildings before you reache the last tower/s in front of the nexus). If you destroy an inhibitor, super creeps will spawn on this lane, which do more damage and have more life than normal ones.But be careful: the lines and towers are protected by other champions.
Here is a gameplay video for you to get a better view over the game:
I hope you try the game and perhaps we meet ingame :)