Featured Snippet is the very first result (0th result) on Google’s search engine result page in a different form than the normal format. They provide the answer to the search query by pulling relevant content from the page.
The featured snippet tells you the very basic answers to the query you are searching for. To get more details, you have to click the link.
Google sometimes shows for certain queries, usually questions (i.e., who/what/where/when/why/how) with featured snippets
Featured Snippets have a higher click-through rate because they provide additional information to users and they naturally click on the link to see further information.
Following featured snippet is for the search query
"how to backup wordpress site"
There are five types of featured snippets named paragraphs, tables, lists, and videos. List can be divided in to two called numbered list and bullet list. You can see them on SERP when you search in Google.
There are no specific markup or format to get displayed as featured snippets. But you can follow the following guideline which may increase your chance of getting your page listed as featured snippets. But none can guarantee except Google.