Don't worry - you don't need one!
All you need to register for Handouts is a unique username. This can be anything that has not already been taken by another user - maybe you have a unique class or student ID, for example. Or you could use a mix of your first and last names, e.g. for the student Jane Smith, the username could be janes, jsmith or janesmith. The possibilities are endless! Just make sure it's something easy to remember and be sure to keep a record of it some place safe :-)
Write to us at firstname.lastname@example.org any time you have questions!