Related search lets you show related search terms when a user makes a search query on your site. When the user clicks a related search term, they're taken to another search results page. Using related search on your search results, you can increase search volume on your site and help users find what they are looking for.
Create a related search unit for your search pages
Before you start, review the Google Custom Search Ads Policy: Alternative Search Queries.
To create a related search unit for your search pages: