You have a reseller hosting account control panel called Web Host Manager. WHM is where you go to create your customer accounts. After filling in their account information you click "create". This will instantly set them up with their very own control panel called cPanel. This is where they will go to administer their website. Once they are logged into cPanel they can create subdomains, email addresses, change passwords, and much more without requiring any help from you or us.

Note: Don't Worry we have some nice tutorials for Starters :)