The key bindings for controlling your chosen champion within an actual match are quite simple and easy to pick up. Move your champion by right clicking a location on the map or minimap. In most situations, your champion will automatically begin attacking enemies when the come into range, but to target a specific enemy, right click on it. In addition to these basic attacks (also called autoattacks) every champion has four(or more in rare cases) skills plus a passive ability. The four skills are bound to the Q, W, E, and R keys. The passive ability is not bound to a key, as it takes effect without any player input (hence passive). The player can at any time return to his spawn point by pressing the B key. This is referred to as backing, going b, or bluepilling. Also, pressing Enter creates a chat bar which you can use to communicate with your teammates or the other team.
There are currently three types of matches available to LoL players, with a fourth coming soon. First, there are custom games, which are typically the most casual type. Players can test out new champions, play with large groups of friends, or set up special types of games with special rules (such as the popular All random all mid game). Next, there are normal games, which are more competitive than custom games. Here you are either grouped with other players according to your skill level, or you may form a team yourself with people from your friends list (called a premade team). Either way, the game tries to match you up against players of similar skill levels so that it will hopefully be a fair game. Finally, there are ranked games, which can be highly competitive and are only available to experienced players. Since this guide is aimed towards newcomers, I will not discuss ranked games.