Each platform has different welcome bonuses, both in terms of content and how they are obtained. The most common formula is for the user to sign up, pay an initial amount into their account and then receive a bonus as a percentage of the amount paid. You must then usually play at least part of the bonus received through the promotion on the site in order to actually withdraw the money from your account. In any case, it is always advisable to carefully read the terms and conditions of every single offer.