These four blocks are very similar. All of them are newer than the “legacy” Context block, and all four support fetching metadata (i.e., title and author information) about the bookmarked, liked, replied-to, or reposted web page or post.
To create a short, e.g., “bookmark post” (well, uh, note), simply create a new note, and add a Bookmark block. In its URL field, type or paste the URL of the page you’re bookmarking.
Then, hit enter (or move focus to elsewhere within the Bookmark block or its sidebar panel). This’ll trigger the block to fetch the bookmarked page title, and any author information.
If applicable, add a quick note directly underneath (i.e., as a “child” of the Bookmark block). Or a quote—simply convert the placeholder Paragraph to a Quote block. Or nothing at all, that’s okay, too!