There are many types of games and sets of rules that people play with hold em. Heres a brief list of the main types of games :-
Limit & Low Limit Hold Em : Blinds are set and are usually set every half hour. The maximum raise per round is set before hand but it is usually one or two times the size of the blind at the game. In a game like this bluffing is not as effective until the later stages when blinds are high.
No Limit Hold Em : No limit is the method used in most major poker tournaments like the poker tour and of course the World Poker Series.
Torunament Games : A set number of partipants pay a fee and are given an equal number of chips to gamble with. The money is divided to the top 5 to 50 players - depending on the size of the tournament. For example, at poker rooms 5 dollar tournament each player gets 1000 to gamble with and the top prize for the winner is about a few hundred dollars - once again this depends on the number of particpants.
Ring Games : In ring games the number of chips you have at the table depends on how much you bring. It is not an equal playing ground like a tournament though this is the most common method of playing hold em in casinos.