cPanel is the name of the website control panel used by many free hosting services and preferred by many users to alternative control panels.
With cPanel you can control many, many aspects of your site including creating database, DNS records, controlling the domains on your account, view overall account statistics, manage files and databases and much more.
To access your control panel you can login via a few places in most cases...
If in doubt, refer to your initial welcome e-mail for exact details as it will be provided in that e-mail.
When you signed up for an account you should have received details regarding your new account including a username, password and other associated information.
It is with this information in the form of zpa_123456 for your username, and of course your chosen or assigned password that is used to login to your website control panel.
If you lost your password please refer to the control panel login area for the 'Lost Password' facility, with this you can reset your password and have it e-mailed to you.
Please refer to your hosting provider website for how to contact support to recover your username.