Here are the all videos to help you map multiple domains on WordPress.
The last video in the series covers setting up Domain Mapping System, so please scroll to the bottom if you've already configured your A Records and added an Alias on your hosting server.
Buying a Domain Name
How to Configure Name Server Records
Setting up Cloudflare
Install WordPress on a Hosting Server
Configuring DNS Records
Configuring Addon Domains, Subdomains, and Aliases
Domain Mapping in WordPress