When you log in on the left hand side you will see an option that says all courses. Click that and you will be able to select from all the courses on the moodle site to register, as long as you have the appropriate registration key.
After you log in, you may change your e-mail address. This is done by locating the profile link on the left hand side of the screen. It is recommended that you change your e-mail because the current e-mail is whatever e-mail address that the student's parents have on file. This can be irritating for parents to receive copious amounts of e-mails about homework or forum posts.