you can either jump on youtube, check out the champions there, see how they play and operate. or you can just jump into games and play diff champions and decide what ones you like and don't like.

I would suggest playing dominion as it's fast paced games so you can have a higher game turn over and spend more time finding what champions you really like.

you also have a skill tree in your profile section under masteries... make sure you keep up with it.