Global Regions are exactly two: the Header and the Footer. You design each once and it shows on every page, including blog, store and course pages.
The page
Each card shows a status (Published, Draft or Not designed yet) and a button: Design Header the first time, Edit Header afterwards (likewise for the footer). It opens the Studio. Regions follow the same draft and publish split as pages; publish from the Studio. There is no unpublish. The badge shows the stored status only, so a published region with unpublished edits still reads "Published".
Opening a region sets it to the site's default language, which also sets the editing direction (right-to-left for Farsi).
What shows if nothing is published
On a theme that uses regions, no header or footer at all; there is no automatic default. A theme with its own built-in header and footer components ignores regions and uses its own, filled from the header and footer menus. Applying a theme normally seeds and publishes a header and footer for you.
Apply Theme replaces them
Applying a theme replaces both regions with the theme's own and publishes them immediately, after saving the old ones as a version. It also overwrites the header, footer and mobile-nav menus. Page content is replaced only if you tick "replace content".
Region-only elements
Some elements, such as the light/dark switch, appear in the palette only when you are editing a region.
Menus and patterns inside regions
A region can contain a saved Menu element (by menu key) and Patterns; deleting a menu that a region uses is refused.
Permissions
cms.read to see; cms.write plus the page-writing plan feature to design and publish. Read-only users still see the buttons and get an error.