At its core, a casino bonus is a set of extra play credits provided to a player under specific conditions. The most important distinction a player must understand is the difference between the Cash Balance and the Bonus Balance. When you claim an offer, the funds are typically placed in the bonus balance.
These two balances behave differently: cash is your own deposited money and is generally withdrawable (subject to standard verification), while bonus funds are "locked" until the terms of the offer are fulfilled. Most platforms utilize a system where the cash balance is used first for betting; once that is exhausted, the system begins drawing from the bonus balance. Winnings generated from bonus funds remain in the bonus balance until the wagering requirements are fully cleared.