Do It Yourself – Website Tutorials
Use custom domain for your Google Sites. This video tutorial will show you how to setup your custom url for your Google Sites. You will need to be using G Suite Apps for business or education in order to do this. Follow these 3 steps to quickly setup your own domain.
Create a CNAME
Publish and name your site in Google Sites
Map your domain address in your Google Apps Admin Panel.
CNAME Record Values: https://support.google.com/a/answer/112038
source