You must have a VPS or Dedicated server with rootWHM to do this.
- Login to WHM and click the Create a New Account link.
- Fill in the infromation as normal, then scroll to the Reseller Settings section.
- Check the box for "Make the account a Reseller".
- You may optionally check the box for "Owns their account (They can modify their own account)".
- Click the Create button and you are done. Your reseller customer can access theirdomain.com/whm and login with the cPanel username and password which you just created.