cPanel is your website's “control panel”. It's where you handle all the administrative aspects of your site - such as managing the files you've uploaded to your site, editing the content in the sidebars of your website, and checking your site's statistics.
In the email you received from ASC Support notifying you that your new site is ready for you, you'll find your username and password for accessing your website's cPanel.
Also scroll down to the “Hosting Videos” section on the Video Training Center Page, and spend some time watching them.