To add a user defined field for lessons please do the following:

  1. Go to Team Profile
  2. Update the Member Field and / or Account Custom Field
  3. Go to Lesson Admin
  4. System Tab
  5. Select Edit in the Bottom right
  6. You can Select whether to enforce this field/hide/or make optional to the registrant.

See Also
Lessons: Can I create/Clone a class with no or a zero fee associated with it?
How do I adust an account in Lessons, reset password or update email/information?
Lessons: Report of account and student information