Are there cPanel User Accounts
Currently there is only one level of cPanel access which is the cPanel username you're given upon sign-up.
Whenever you add an additional domain or subdomain, you choose the FTP details for that particular domain. You can also create restricted FTP accounts. Click here for a guide on doing that:
With those details, you can login to the server using FTP or SFTP and the login details will only provide access to the files for that particular domain/subdomain.
If you want to provide access to a service that is accessed through cPanel, phpMyAdmin for example, you would need to either perform the actions yourself or share your cPanel details (which we don't encourage).