Every time I try and watch a video, a payment form comes up
The site puts up a signup form when the user is not yet a member and tries to watch a member-only video, and puts up a payment form when the member has not yet completed the payment portion of joining the site.
If you are not yet a member:
Signup for membership and fill in your email and password, then continue to the payment form to complete your membership.
If you are already a member:
Login to the site and complete the payment portion of the signup process: