hi,
once u have place reserved on your chosen module, to complete registration you need to fill in registration agreement wchih you may download from your student home page or it will b sent to you, you need yo fill it in and send it back to open uni. if you want to appy for saas you need to download and fill in their application and send it with your registration agreement and any other needed documents for your saas to open uni. then they will fill it in and send it straight to saas. then you will b registered for your module.
hope it helps