A shared section is one section used on many pages and edited once - change it on any page that uses it and it changes on all of them. This screen is the list of them, and it is where one goes live, is rolled back, or is deleted.
The screens pictured here are an example ministry’s, so the names and figures in them are not yours. Everything they show works the same way in your own admin.
Open Site, then Shared Sections.
Edit opens the first page it is on, where it is edited like any other section.
A section on no page has nothing to open; add it to a page first, from that page's Add rail.
Press Put Live on All N Pages (Put Live on Its Page, for one) when the row says Changes waiting.
One press, every page at once. Discard beside it throws the waiting changes away.
History shows every version that has been live; Put This One Back loads it.
It comes back as waiting changes, so nothing reaches the site until you put it live.
Delete removes the section from the list.
Refused while any page still uses it - the button says why - so take it off those pages first.
To make a shared section, open any page, then the section's menu, and choose Make It a Shared Section…. To use one, add it from the Shared sections shelf of the page's Add rail.