Social media tab allows you to determine how the page is displayed when it's shared on social media.
Social media tab
Previews for social media posts are also available for Facebook/Twitter
The page title, without the site address or site name
A description of the page content consisting of at least two sentences
An image that is displayed with the shared content
It might take a while before the changes are visible to social media shares, read more:
I updated my pages to share on social media, but the information doesn't update properly on social media channels when I share the page?