Webmentions are a useful way to notify a website that you have linked to it. Microformats like h-entry combined with u-in-reply-to, u-like-of, u-bookmark-of, or u-repost-of give context to the mentions.
Sending a Webmention means POST-ing to a Webmention endpoint with the data source and target. The source is the URL of the page that contains a link to the URL target. Note that a standards-compliant recipient will discard Webmentions if the content of the source page does not contain a “per-media-type” mention of the target URL. For example, and HTML source might contain an <a href> or <video src> matching target URL and a JSON source could contain any key whose value exactly matches target. A plain text document would need to contain the target URL verbatim.
While simply notifying a site that you’ve mentioned or linked to it is nice, without additional context the Webmention might not be very useful. Adding context using h-entry, ideally with embedded [h-card]s.(https://microformats.org/wiki/h-card)