Click on Enroll Users to the upper right of the screen.
In the Assign roles drop-down list box at the top of the dialog box, select the appropriate role.
In the Search field, type the user's first or last name. Select the user and the name will appear in blue above the search area. You can select multiple users to add.
Click on Enroll Users.
You can now return to your course by clicking the link at the top of the page.