Using your web browser,
1) Go to http://www.yourdomain.com/webmail
2) Log in using your username and password.
3) Click on Horde or SquirrelMail
It’s that simple.
*Optional: if you have Outlook, after logging in using your web browser, click on “Configure Mail Client”, then choose “Auto-Configure Microsoft Outlook 2000® for POP3 Access” to automatically have cPanel configure Outlook for you. This involves downloading a registry file and installing it. If you would rather not do this or the auto configuration doesn’t work, then follow the manual configuration instructions.
Final Thoughts: I suggest using Outlook if you have it.