To point a domain to heroku application, first add a domain to heroku application under Your Application > Settings.
Once domain is added, you will see DNS record like
You can login to your domain/DNS provider, add a CNAME record for www and point to the heroku domain provided.
For domains with out www, you cant point to a CNAME. If your domain provider have option for URL forwarding, you need to forward the URL to http://www.yourdomain.com