cPanel is a web based hosting control panel used to manage websites from a web based graphical user interface (GUI) from which you can control you portion of the Unix server.

The tools provided are designed to simplify running your website. It uses a tiered structure that allows different levels of access so that administrators and end users can control the different aspects of the website directly through a web browser (Firefox, Chrome, IE, etc.).

For detailed information, check out the official cPanel website.