A year ago I tried learning ActivityPub, and more or less failed. I was confounded by a spec that was so abstract I couldn't make heads or tails of it. Turns out I was missing some key things.
I have written a guide to learning about ActivityPub that I wish existed a year ago when I first set out to learn how to write social media servers that conform to the spec:
This Mastodon instance is for people interested in technology. Discussions aren't limited to technology, because tech folks shouldn't be limited to technology either! We adhere to an adapted version of the TootCat Code of Conduct and have documented a list of blocked instances. Ash is the admin and is supported by Fuzzface, Brian!, and Daniel Glus as moderators. Hosting costs are largely covered by our generous supporters on Patreon – thanks for all the help!