This is an RSS service for Mangadex, since they had one in v3 that I made liberal use of, and I've heard nothing regarding its return in v5.
If you've never used RSS before, I strongly recommend starting, as it's the second-best update notification system in existence (and it could be built on #1, push notifications, but that's an another topic).
You will need an RSS reader program, but your browser probably has one built in, so you can just use that. (I don't recommend it, because you should be closing the browser more, not less.)
The important part of an RSS feed is a source URL. If properly configured, that should provide everything else. In this case, you've already found the source URL... Kinda. You need to pass a manga ID (or several) to make it work. A manga ID looks like this: ed996855-70de-449f-bba2-e8e24224c14d (yes, that's a UUID4). If you go to a manga's page on Mangadex, you should see something like it in the URL bar at the top. I think Tachiyomi has some way to grab it, but I also think Tachi's update notifs are better than mine, so if you have that you don't need this.
Once you have the ID(s), you should palm them into this page like this: https://rakka.tk/md.rss?ids=ed996855-70de-449f-bba2-e8e24224c14d. Take that and give it to your RSS reader as a new feed and it should handle the rest (did your browser ask you a new question when you clicked it?). If you want more IDs, put an & and do it again: https://rakka.tk/md.rss?ids=ed996855-70de-449f-bba2-e8e24224c14d&ids=d032cdeb-1ced-4031-8b9e-45e6064c1781.
It behaves a bit differently with 1 ID vs multiple, but it should work alright both ways. Personally I prefer making one feed for each series.