A pattern is a block you design once and reuse on many pages. Pages link to it, so editing the pattern updates every page that uses it.
Making and using one
Patterns are created in the Studio: select an element and Save to library as a Pattern (linked) (the other option, Template (copy), saves an independent copy). Insert it from the Templates panel under Patterns. On the page it appears as a Pattern element; Edit pattern opens it and Detach from pattern turns it into an ordinary copy.
The list
Each card shows the name and Used on N page(s) (pages whose draft or published version uses it, header and footer included). Rename (also renames all language versions) and Delete pattern are on the card.
Language versions
Under Edit in the builder there is a button per existing language, and + code for each site language that has no version yet. Adding one copies the default-language version and opens it. On the site, the page's language is used, then the default, then the oldest version.
Editing is live
A pattern version is live as soon as you save it, with no draft or publish step, on every page that uses it.
Deleting
A pattern still used on a page cannot be deleted ("This pattern is used on N page(s). Detach it from those pages first."). Deletion is permanent and removes all language versions. A pattern cannot contain another pattern. A page that points at a missing pattern simply shows nothing there.
Permissions
cms.read to view; cms.write and the page-writing plan feature to rename, delete and add versions.