Before you are able to withdrawal any money awarded as a bonus, that money must be wagered 35x. With most online video slots having around a 96% theoretical Return to Player (RTP), it only takes a little bit of luck to surpass those wagering requirements and convert that bonus money into real cash available for withdrawal.
Because some games have extremely large RTPs, such as blackjack, not all games count towards the wagering requirement and some count only partially. Please see Wildz’s Bonus Terms for full details on the different games and their bonus contribution levels.