The primary UX between servers is the "local feed." This is a feed dedicated to all posts within the server. You can't really access that feed from outside of a server. That's pretty much it. You can follow people on other servers, at-metnion, etc.
Many servers allow their Local Timeline to be browsed by anyone. From the server's home page, click the "Local" button to the top-right. If you find a person or post you want to interact with, simply copy and paste its URL into the search bar of your app or home server.
I guess my month-long moratorium on bothering to contribute to any Fediverse-related conversation on HN needs to be maintained for a bit longer. Change is painful for many, particularly when they didn't think of it, or can't profit from it.
Starting your own server is a waste of time, imo.