Just like any other offline casino would do, an online casino also offers a sign up bonus or online casino deposit bonus. There are certain rules associated with an online casino deposit bonus just as there are with a deposit bonus with an offline casino. The bonus that is offered to you is dependent upon the method of deposit. Usually bonus amount is a percentage of the deposit that you have made. Say, for one casino the deposit bonus may be 50% with $500 max. That means that when you make the first deposit, 50% of that will be credited to your account as a deposit bonus. If you deposit $1000, you will get $500 as a bonus. However you will never get more than $500 as a bonus. That is the maximum amount.
Another rule is that the deposit bonus that you have made cannot be withdrawn unless you have made a specific wager. For example in some casinos it is a rule that you will have to make a wager of 10 times the first deposit and the bonus amount before you can withdraw your bonus. The best casino bonus offers can be found here or if you want to find out more about the different online casino games, try your luck at Zodiac Casino. Those websites should give you a good idea of where to start with online casinos.