Tom, for the basics of what Webmention is you might try this intro article Webmentions: Enabling Better Communication on the Internet.
To get started quickly, just to have the notifications, you might try creating an account with Webmentions.io and put the endpoint into the
<head> of your site so you can receive them in the erstwhile on a separate service and worry about direct integration at a later date. As I recall Aaron Gustafson has a Webmention.io Jekyll Plugin for display and some of the outline is covered in this recent article by Max Böck.
If necessary, you can get help in the #Dev channel of the IndieWeb chat.