The Bandwidth stats shows an overall summary of the bandwidth usage of your website. This bandwidth stats shows usage of HTTP traffic (i.e. viewing web pages in your website) and possibly FTP upload/download traffic. However, the stats does not include email traffic (i.e. send/receive email from your email accounts).
To check your website bandwidth usage:
Click Bandwidth link in the Web/FTP Stats option in your Cpanel hosting account control panel.
Bandwidth usage summary is presented.