1. Open up your favorite browser and navigate to http://example.com/webmail, replace "example.com" with your domain name. Enter your full email address and password in user login details and then press the "Login" Button.
2. You will be redirected to a cPanel Webmail Page. Click on any Webmail Email Reader like "Horde", "Roundcube" or "SquirrelMail". I personally prefer Roundcube as it has a nice interface and is easy to use. You may enable "AutoLoad" if you prefer 1 over the others.
Once your Webmail Email Reader opens, you will be able to read and send emails.