First, click on Manager, then click on My Courses.
Next, click on the name of the course that you want to add a user to.
Next, just click on the Add User button. This will bring up a form that you can use to add the user. The Email field is checked first -- if a user with that email already exists in the platform, then that user is simply added to the course. If the user does not exist, an account will be created using the information that you entered, then they will be enrolled in the course.