The difference between Limit, Pot-Limit and No-Limit games is in the betting amounts.

Limit games

In limit games, the only valid bet/raise is fixed by the table stakes. During the first two rounds, all bets/raises are equal to a number called the minimum bet, and during the last two, bets/raises are equal to the maximum bet. For example, $5 on the first two rounds, and $10 in the last two rounds in a $5-$10 Hold'em game.

Pot-Limit games

In pot-limit games, a valid bet/raise must be at least as much as the previous bet/raise in the same round. For example, if the first player to act bets $100 then the second player must raise a minimum of $100.  A pot-limit bet/raise may be at highest the value of the pot, plus all bets at the table including the current player's call. No maximum number of raises exists.

No-Limit games

In no-limit games, a valid bet/raise must be at least as much as the previous bet or raise in the same round. No higher limit is available, other than the players’ available amount. No maximum number of raises exists.

All-in and side pots

When a player puts the last of his chips into a pot, that player is said to be all-in. An all-in player is not eligible to win any money bet after his last bet. The excess part of the bet is either returned to the lone bettor, or is used to form a side pot with another player or players still remaining. There is no limitation on the number of side pots. The all-in player(s) will be eligible for the pot they are involved in and cannot be forced from the hand.