You can search for users and add them manually to your Moodle courses. When you are doing so, make sure to check what Role you are giving to them in your site. Do not give users more than one role in a site. The privileges of the lesser role will override the privileges of the higher role.
Instructor - Instructors can do anything within a course, including changing the activities and grading students.
Designer -A duplicate of the Instructor role. This role is intended for those who are designing the course, but not instructing it. Designers will not be listed in the Course Description or in the Participant List.
Teaching Assistant - A duplicate of the Instructor role. This role is intended for those who are supporting the course, but not instructing it.
Non-editing instructor - Non-editing instructors can teach in courses and grade students, but they do not have designer capabilities, thus they may not alter activities (e.g. teaching assistants).
Locate Settings block > Course administration area
Click Users link > Enrolled users
Click the Enroll users button
Type a name or email of the user in the pop-up window, click enter key on the keyboard.
Review the "Assign roles" drop-down to ensure that you are assigning a proper role to a person. Click Enroll button. Once you are done, click Finish enrolling users button. The pop-up window will close.
Role changes only take effect after the next log in from the user. If you assign a role to a user, or override any of the roles capabilities, the user must log out from the Moodle system completely and then log back in, in order to see changes.