To manually add a Learner to one of your courses, navigate to the the Learners page from the sidebar.
Click on the Add button at the top of the page.
A pop-up will appear -- enter the Learners name, email address and what Course or Bundle you want to assign them to, by clicking the space underneath (Course Name)
Your learner is now on the system and will have access to take the course.
Note that you will not be able to add Learners until your course is Published.