In Limit Game both Bet and Raise are preset.
For example, in 5/10 Limit game, in the fist two betting rounds Bet and Raise must be equal to 5. Not less, not more. In the last two rounds Bet and Raise and raise must be equal to 10.
Pot Limit game
In Pot Limit game the maximum value of Bet and Raise must not be more than the current pot amount.
For example, if the pot amount is equal to 30, a player can not bet more than 30.
If the player raise the bet of the other player, in that case a call is already included in the pot. It means that if the pot amount comes to 100, player X bet 100, player Y bet 300 raising by 200 (Pot = Initial 100 + Player X's 100 + your 100).
No Limit game
In No Limit game there is any bet limit. Every player makes any bet in any betting round. Minimum bet is equal to Big Blind.