You can access webmail without logging into your control panel. This is handy if you have employee's that need to access webmail as it only allows them access to their own mailbox and not the full cpanel.
You will need to setup your required email accounts using cpanel before you try to use web mail otherwise there will not be any mail accounts for your users to log into and you will not be able to login using web mail.
You can access your webmail with this URL:
yourdomain.com/webmail/ or yourdomain.com:2095
(Dont forget to add the last trailing slash onto /webmail/ otherwise you may get a [Page cannot be displayed] error.)
This will prompt you for your login details and you will need to enter your full email address and email password. This next screen gives you several email applications choices to choose from. Choose which one you want and click on it.
If it is the first time your using this application you will be asked a few simple questions after this you will be taken to the webmail page.
Ideally you should avoid using the Webmail icon from the main page of your control panel as this will take you to the default account which use's your cpanel login name and you will be unable to change this, and may not see proper mailbox emails.
You can also login to your web mail using just the control panel username and control panel password which will enable you to read all incoming mailboxes for all users, but you should NOT try to send out email using this login as there is not way of controlling this login due to it not being a proper mailbox, so if you do use it, just use it only for reading all emails, never sending.