After filling registration form on the site, the casino gives a new player a small amount of money to start playing with (usually $25 or so). When the player wants to withdraw the winnings, he or she will have to show 10-12 times the initial sum wagered before he can do so.

A Player receives a reward bonus for depositing his or her own money.
If a 100% bonus has been offered, this means a $100 deposit will convert into a $200 casino credit. The size of the bonus that a player receives depends on the time of the deposit (1st, 2nd etc) and on the amount of the deposit.

Bonus Terms

1st Deposit – This is a Beginning or a Sign-Up Deposit which the player receives at the start when he or she enters the online games such as online blackjack etc. 
In some cases the casinos will not let the player get winnings back before gambling several times the initial amount.

2nd, 3rd, 4th Deposit Bonuses – By continuing to deposit into the casino's account, a player will be awarded further bonuses which are usually within the 25-100% range. There is no limitation on cash-outs.

High Roller Bonus – Players who spend large sums in a casino will receive even higher bonuses. These can reach 1000$ and even more.  

Online Tournaments – Each player pays a small entry fee to join a tournament. All this money is pooled into a large pot, which only a few people will win. So for an small entry fee, a player can potentially win millions.