How do search engines like Google know which site domain is the right one? [WP Empire Builder]

Let's say your "mother" site is:

mothersite.com

Let's say your "child" site is:

childsite.com

The way WordPress multi-site (and thus, WP Empire Builder) works, it will actually have TWO (2) valid URLs for your child site:

childsite.com and

mothersite.com/childsite-com

You may notice this in permalinks, or when creating new posts.

However, we use "canonical URL" to tell Google and other search engines that the "right" website is childsite.com.

ONLY childsite.com will appear on search-engine results.

Your site will also be AVAILABLE as mothersite.com/childsite-com but it will never appear on search engine results.