Here’s a handy video which highlights both single user creation using the Administration “Add new User” option AND the bulk upload of users by CSV. Both are very necessary skills for anyone administering their own Moodle site from a free or hosted service. Check out the great video/screencast embedded below and be sure to check out Moodletuts.com for more videos in the future.
For more information about bulk uploading of users be sure to read up in the Docs/Help on your site (the little (?) buttons) or the Moodle docs: http://docs.moodle.org/en/Upload_users.
Direct video link: http://www.screenr.com/FUx.