After registering your account, you will be required to verify your identity. Unless you complete this process, you will not be allowed to withdraw your winnings. To complete this process, you need to submit documents that will prove your identity. Your options to send it is through email, fax, or post.
Ideally, you only have to do this once. However, if you plan to withdraw a huge amount, you might be asked for additional verification. This will be for security purposes and will not be as thorough as the first one.