You need to have an account on a casino or their affiliate site for you to promote their platform, you will be given a special link that you can use to sign up people that you refer, and once they sign up you will be rewarded on all their action, it could be from their wage, from their deposit or from their rank, it all depends on the rewards the casinos are giving or you have the option.

Casino affiliates is one of the hardest to promote because you cannot promote them on social media platforms because they restrict people from promoting vices like gambling, so you have to do research to find places where you can promote your link.