After adding email accounts, you can check them through cPanel's built-in webmail clients (Roundcube, Squirrel Mail, and Horde Mail) by going to the following:
After logging in, you have to choose which webmail client you want to use. Choosing is just a matter of preference, but you can view their differences in cPanel's documentation, Which Webmail Application Should I Choose?
If you need to reset the email account's password or would like to change it, see Change cPanel Email Passwords.
Note: All email addresses on a cPanel account share the same pool of 500 SMTP relays (outbound messages) per hour.