If you are accessing email from an email client such as Outlook you will need to enter your email account details before you can send/receive email.
This information is also included in your original account activation email and available from your client area:
Incoming Mail Server (POP3): mail.domain.com
Outgoing Mail Server (SMTP): mail.domain.com
Account Name: [email protected]
Password: email account password
You need to substitute "domain.com" with your actual domain name. "[email protected]" should be substituted with the full email address you have setup and the password is the password you entered when setting up the email account. If you forget the email account password you can always reset it from your cPanel control panel.