Originally Posted by Lume

In an essence, League of Legends is a rapidly growing DotA clone that inspires to have it's own unique heroes, mechanics, maps and feel then the normal revamped DotA clones such as Heroes of Newerth and DotA 2. It follows the standard gameplay mechanics that you and 4 other players go against another team of 5 players, all using "champions" that level up throughout each game, gaining ability, item and stat levels. The overall goal is to push the towers of the opposing team and destroy their nexus.

The game is huge. Tournaments, sponsorships, live streams and advertisements are to be found everywhere about this game and that's most likely due to the more casual feel while still catering to the hardcore competitive MOBA players. About 30 million users were counted as registered in April 2012 but it's possible a few hundred thousand are "smurf" accounts or alts.

When you start the game you'll be prompted to enter your experience with past MOBA games, pick your summoner icon and enter your name. Your experience with past MOBA games will help judge what players you're matched up with to begin, your summoner icon can be changed whenever you want and your name can be changed through purchasing Riot Points with real money.

Anyways, you have a level that follows you through your whole account life, being your summoner level, and it will help determine what "runes" you can use, summoner spells, certain features like ranked games and unlocking a point you can assign into a skill tree up until level 30, being the max.

A warning before playing, most people you find in-game will be extremely rude and ignorant so it's suggested you play with friends if possible.

I also suggest that when beginning you try to do some Co-Op Vs AI, allowing you and other players to go against bots, letting you familiarize with the game mechanics.

That's pretty much the gist of the game and I'll help you guys get started by providing some somewhat in-depth roles and what you should be looking to do, along with in-game terms that you'll find when playing.