When you go to register for a course, the information about the course is repeated, so you can tell if you clicked the right one, and so you still have access to the information links.
Since there's no shipping, and hence the results don't depend on your address, it can all be accomplished in one step—just fill in your address and credit card number, and away you go! This page is, of course, cryptographically verified and secured (as shown by the "https" URL).
If something you enter is unsatisfactory, like you omit a required field, or if your credit card doesn't verify, the error message will come up in red, like the one shown (which is shown the first time you get to the page, before you fill in and submit any information).
When you successfully submit your personal and payment information, and if the course isn't full (other people can be entering their own registrations at the same time you are, so a course that had spaces when you looked might be full by the time you've decided to register and entered and submitted your information), you get a confirmation screen (not shown, because it's not interesting) confirming that you are registered for the course.