Bet as well as raise is agreed in advance. For example, in a $1/2 Limit game, in first two rounds both bet and raise must be equal to $1. In last two rounds bet and raise must be equal to $2.
The maximum bet and raise shouldn't exceed the current pot amount. Maximum raise is the size of the pot, which is defined as the total of the active pot plus all bets on the table plus the double amount the active player must first call. For example, if the pot amount is $10 and the first player bets $10, the second player could bet a total of $40:
$10 is the active pot;
$10 is the bet sum on table;
$20 is the double call.
There is no maximum bet limit. Any player makes any bet in any betting round. Minimum bet is equal to big blind.