Custom Domain Step 1: CSR
The first thing you will need to do in order to set up your domain is purchase a Wildcard SSL certificate. The wildcard certificate ensures that not only is your primary domain secured, but any subdomains you may want to use are also protected with SSL (e.g. blog.example.com, support.example.com).
Before you can purchase your certificate, however, you will need to generate a Certificate Signing Request. This file provides all of the necessary information to your SSL provider, in order for them to issue your certificate. Generating the CSR is a simple process of filling out a brief form, and can be done directly from your admin dashboard.
Log in to your admin dashboard and navigate to Settings > Domains > New CSR
Completely fill out all fields, keeping in mind that they generally refer to your organization.
Notes: when it asks you for your country, that should be the country where your business or organization is currently located. Also, the common name will need to be specified as *.[yourdomain].com, such that if my domain was www.example.com, I would enter *.example.com in the common name field.
Be absolutely sure not to lose any of these files, as you will need them at a later point in the process.
It will create a ZIP file. When you open that zip file it will then create a new folder containing the 3 files mentioned above. For now, you should open up your CSR (*.example.com.csr) in any plain text editor (notepad for Windows and Text Edit for Mac), and copy all of it's contents exactly as they are (do not modify this file).
When ready, move on to Step 2: Purchasing an SSL Certificate