No Limit
In No Limit games you can bet any amount from the amount of the big blind upwards on any betting round.  When two amounts are used in reference to a no limit game (like "$3/$6 no limit"), these are: "$small blind/$big blind". The minimum bet is the larger of the two numbers, and the maximum bet is the total amount of chips that you have.

Pot Limit
In Pot limit games you can bet any amount between the big blind and the pot size on any betting round.  When two amounts are used in reference to a pot limit game (like "$1/$2 pot limit"), these are: "$small blind/$big blind".  The minimum bet is the larger of the two numbers and the maximum bet is the amount in the pot at that time.

Limit
In Limit games the amount you can bet each round is set beforehand.  In a $5/$10 game you bet $5 at a time.  On the turn and river, the second number ($10) is the only amount that can be bet.  There is a limit of four bets per player per betting round.