1. The raise amount must be at least as much as the previous bet or raise in the same round.
2. The size of the bet is determined by the pot in the middle, including all bets on the table and the amount the active player must first call before raising.
3. For Example if the pot in the middle has $20. Now the first player bets $15, the second player calls $15 and your call is $15. At this moment the total amount in the pot before your raise is $65.
4. Now you may either call $15 or you may call and raise anywhere from $15 to $65. Remember you can never bet more than the current size of the pot.