The player character takes the place of the actual player in the game. The character has detailed characteristics, from the important (endurance, strength, etc.) to the trivial (favorite color, height).
It is generally a good idea to not play the stereotypes unless it is required. They get boring after a while for most people. Usually a character that has little quirks - a three-dimensional character who's as complex as anyone you know - is more interesting.
A player character provides the player a chance to be wild, to do things that could never be done in reality. Of course, one stay within the limits of believability in the game. A good idea is to ask one's gamemaster for more details.
In contrast to player characters, a non-player character (NPC) is a character in an RPG that is not controlled by one of the players.