TYPE            HOST    URL (in browser)         DOMAIN (served)
======================================================================
A Record        @       example.com        ->    104.197.12.54
----------------------------------------------------------------------
CNAME Record    www     www.example.com    ->    example.com
----------------------------------------------------------------------
CNAME Record    blog    blog.example.com   ->    example.herokudns.com
======================================================================

URL IN BROWSER                                ACTUAL CONTENT SERVED
======================================================================
www.example.com    ->    example.com    ->    104.197.12.54
======================================================================