To use your own custom domain/subdomain instead of the default one, all you'll need to do is create a free account with Cloudflare.com, follow their instructions to setup and import your DNS settings, and add an "A" record like below. (Note: You may replace "pages" with whatever sub domain you'd like to use):
By doing so, your subdomain "pages.yoursite.com" is now pointing to your Capture account.
Please make sure the "cloud" icon under the "Status" column, is grey instead of orange, you can switch the status by clicking on the icon.
If you want to use the main domain name, instead of adding a new "A" record, just edit your main domain name record and make it point to the following IP address : 18.104.22.168.
After completing the DNS configuration part, click on "New Domain Name" and register your domain name from there.