From here you can choose between using your HowNow subdomain (yoururl.learnhownow.com) or to use your own custom domain.
To use a custom domain, navigate to your domain host. This is where you purchased the domain from.
In the DNS records, you need to point the A record for your @ domain to 18.104.22.168
Then you need to set the CNAME for www to yoururl.subdomain.com. Where 'yoururl' is your current subdomain.
Once you've done this, go back to the Domain page on HowNow and enter in the custom domain. Then click Verify to connect your custom domain.
Please note: You may need to wait between 2-3 hours for your registrar to refresh the domain.