Be sure to set up at least one account under email accounts before accessing webmail. Once you click on the icon it will give you the address to log onto directly in the future.
You can also get there by clicking the icon below the message. Next you will you will be asked whether to allow it to load your mail automatically.
Just let it proceed. There is normally no reason to turn off auto-loading of mail unless one of your email accounts gets so much mail that it slows everything down.
You will be presented with a choice of interfaces to use; at this time they are – Horde, Round Mail , or Squirrel Mail. If you are already familiar with one of these interfaces you will probably want to use it. If not then use a different one each time until you find the one that you prefer. If you have another web-mail interface that you like, such as Gmail, you can forward some or all of your email there. If you prefer to use a mail client such as Outlook, you can obtain the address of the mail servers for your account from support at your host and configure the e-mail account through your mail client. (You can contact support at Internet Server right from your cpanel).
Then you can download and open mail addressed to you at your domain name just as you would with any other email account.