How does Google Snippet work?

Google’s search results sometimes show listings where the snippet describing a page comes before a link to a page, not after as with our standard format. Results displayed this way are called “featured snippets.”
We display featured snippets when our systems determine this format will help people more easily discover what they’re seeking, both from the description about the page and when they click on the link to read the page itself. They’re especially helpful for those on mobile or searching by voice.
Featured snippets commonly contain one listing, but more than one may appear.