Assuming your students are already enrolled into the Moodle, if they are not then look here for advice on how that can be done using a csv file or perhaps your network guys can set it up using ldap. Assuming you are the Teacher of a course, or an Admin of your Moodle this works.
In the event the students are enrolled into your Moodle then you can use manual enrollments, which is actually simple. When the course is created, it should automatically take you to the Enrol Users page. Click the button on the right, above the enrollment listing, and that will bring up the dialog. In the Search box, enter the surname and press enter, DO NOT click the button, that closes the dialog. Once you have the right person, click the "Enrol" button to the right of the name, and enter the next name.
If the course is already created, when you turn editing on, the menu on the left of the page should have a Users item, click that and then click on Enrol Users. Go through the process outlined above.
Cheers..