What is the use of search_query table in magento 2?

In Magento 2 search_query database table store the search query, which users have searched using the search box in Magento 2.
— query_text field in a search_query table in stores the value of search string. When User search through site, all of the search entry will be added to search_query table in query_text field.
num_results field used for Number of results for specific word in the site. That field show count of any string search in site.
— popularity field is displayed popularity of specific word in your site, the Biggest number will have the most popular search word for your site.
store_id will show search from a specific store.
There are some other field also available in search_query table but above field is the main field of a table.

You can check from the admin panel, all of the search query will be shown from Search Terms sectino.
Click on Marketing -> SEO & Search -> Search Terms
You will get all the search result grid for your site.