Confusing mention process

I am a tiny bit confused as to how I can verify the plugin works.

• I have installed it
• I have activated it
• I have done minor configuration

What I’m missing out on are documentation to verify the Webmentions work. I have looked at the Vimeo video that you reference in one of your FAQ responses, while finding some parts on my posts, and other parts as URL:s that came with the plugin.

I understand this plugin as enabling a Webmention in one of three ways

1. Someone links to a post from my blog
2. Someone adds a URL to a page that has my post URL in it
3. Someone goes to my website’s [whatever whatever]webmention/1.0/endpoint URL

The results I’m getting are these (taken from the numbered list above:

1: I can’t get the “automatic” Webmentions to work. I’ve tried to set the page up in such a way as to follow the Vimeo video, but no matter how I post or fiddle with the settings, I can’t get a post within my WordPress installation to generate a comment/mention by referring to another post in my WordPress installation. It just doesn’t appear.
2: I can make a Webmention work here, by referring to a page containing my post’s URL. It’s a tad cumbersome and the “Help text” section that has to be written for a visitor to understand what they have to do, needs to be carefully and thoughtfully written.
3: I can make a Webmention work here, by referring to the new post containing the URL to an old post, and inserting them both here, sort of forcing them together. Even though this is a super clunky way of doing it, it works.

So, the problems I’m having are related to bullet 1; which incidently should be the one that requires the least effort from myself, and someone wanting to Webmention my content.
I’m using WordPress 5.0.3 and recently switched to TwentyNineteen (although I’m assuming the theme doesn’t matter here).

Any thoughts about this?