This depends on how the course is set up. Some institutions automatically register students. Other use the self-registration method.
You will need a valid email address so your registration can be verified.
Note that the appearance of Moodle changes depending on the organization that is using it. As you work through these panels look for the main sections and most menu items. These will be common to almost every Moodle installation, only the general appearance and color schemes will be different.
A good user name is general your first name, a dot, and your last name. Keep everything lower case to make things easier to remember.
A good password should have UPPER/lower case letters, some numbers, and a special character such as # or ! or $.
Keep the password memorable. For example, your first pet's name (using UPPER/lower case), an exclamation mark "!" and the last four digits of your first phone number.
Use a valid email address. Moodle will be sending a verification email to this address. You may have to check your SPAM folder to see if the email is hiding in there.
If you do not get an confirming email contact the instructor and he or she can confirm your registration.
Once you are registered you will be returned to the login screen.
If you have confirmed the email you received from Moodle you will be able to login. If not you will see a confirmation screen reminding you to check your email.
Sometimes a course will ask for an "enrollment key". This is a one-time check verifying that you have the right to access this course.
If you don't know the enrollment key ask your instructor or the course manager.
If the Learning Activities are hidden and all you see are the module topics, click on the small square boxes on the right edge of the center panel. This will collapse/expand the learning activities.
Use the Forum to make comments, ask questions, or post interesting links for the other students. You are encouraged to respond to other students postings and questions or to add your own thoughts to their comments.
Here is a play-by-play showing how to register as a new user in Moodle.