This web site uses Moodle, which is a web-based Learning Management System.
Moodle uses the email address you provide to both let you securely register for an account on the site, and to let you reset your password should you lose or forget it.
Having your own account allows Moodle to keep track of where you are in the courses you do, and allows you to stop in the middle of quizzes and other activities and then continue them later.
Eventually, we may have courses where your email address is used to contact you in regards to course activities (such as forums, for example), but it will be up to you to participate in these or not.
We have no interest in your account or your email address except for the above, and we have no connections or affliations which might ever cause us to share any of your details with anyone else.
Having said that however, if you want to be sure about your privacy and anonymity, use a throw-away email address from Google or similar to register here the first time and then make sure you don't lose your password.
It's also a good idea to edit the profile settings for your BDSM Workbook account as soon as you have created it to make sure that other users of the site only see the information about you that you want them to see.