The most common form of bonuses offered by casinos are known as a welcome bonus, new player bonus, 1st deposit bonus or sign up bonus. They normally come in the form of a 100% match up to a certain amount. For example, Casino offers you a 100% welcome bonus up to £500. This means that if you deposit £500, you will receive £500 free giving you a total of £1,000 to play with.
In terms of levels of welcome bonuses, they range from 50% up to 500% in some cases but as stated, the most common % is 100%. Anything above 200% should be looked at carefully as there may be a lot of restrictions when it comes to withdrawing the bonus itself. In order to claim these bonuses, casinos sometimes specify you use a bonus code or coupon.