Squarespace is a website that allows you to build website easily, without the need of any prior knowledge of HTML/CSS.
Squarspace offers many services, like domains for sale, their easy to use website builder, and they also offer experts to help you design your enterprise site.
You can see your owned domains here
Go to advanced settings
Here is where you can assign subdomains, point/forward subdomains
To verify your domain, you will need to have this record in the dns management
Refer to the Google Search Console page to learn how to get to this step
For your custom google site url
Save and give it time to propogate