Many courses/communities require an enrollment key. There’s an easy way to get them. First, you must have an account on this server. If you do not have an account, create one before you proceed.
Assuming you are logged-in, click a course category. Clicking a category below will present you with a list of available courses (note: some courses are not open to the public) and a list of instructors/managers to the left. Click an instructor's/manager’s name and you’ll be presented with their profile page. Look for their email address and click. A new email will be created in your email application. You can then ask the instructor/manager for the enrollment key. If you don't see an email address, try the next instructor/manager for the course/community.