Can the users on my account access their own control panel?
Yes. They can use http://www.example.com/user/ (Replace example.com with your domain name).
They would then need to enter their user name and the password you gave them when you created the user, unless they have since changed it.
Once logged in, they can alter their email settings, including setting up spam filtering, take backups, change their password and view their disk usage for the account.