What is cPanel?
When you sign up for an account with a new web host they will usually install it for you. It is a web based application or program that lets you control the settings of your website and it is being used by most web hosts.
cPanel is a very user friendly application that has an icon based interface which can be used to modify email accounts. So you can add remove or edit an email account on your site depending on the restrictions of your hosting package. You can also set up auto replies and email forwarders, setup CRONs, manage your database, modify files directly etc.
The features that you can access depends on the web package that you have chosen and the restrictions or limitations applied by the web host . Usually you will only be able to setup a fixed number of email addresses. This number is usually shown in the cPanel of your site.