Web mail provides you good way to read your mails on the go, any where in the world on any of the computers. You can check web mail as under:-
Cpanel Server:
http://www.yourdomain.com/webmail/ or http://www.yourdomain.com:2095
Here you will get a login window, use your email address as user name and password related to the email address as password.
Here you will have option to select one of the email clients.
You can see related vidoe help at http://www.cpanel.net/media/tutorials/emailaccounts.htm
DotNet Panel:
You can access mail at http://webmail.domainame or https://cmx1.my-hosting-panel.com.
Select any of the desired email client.
Login using your email address and password of related email address.
Related Article:
How to set up web mail to go directly to Horde, SquirrelMail or RoundCube?