Don’t follow the link directly. Click on ‘Communities’ at the top of your page. In the search bar, enter the full community url, i.e. https://lemmy.ml/c/thruhiking. Click ‘Search’. Most likely nothing will happen immediately. When you clicked Search, your instance started fetching posts from the thruhiking community on the lemmy.ml instance and storing it on your beehaw.org instance. Give it a second and click search again. You should now see the community in the results. Click it, and you’ll go to the community through your instance, keeping you logged in and able to subscribe and all that stuff.

This process only has to happen if you’re the first person on your instance to search for that particular community.

Generally, you can subscribe to them from beehaw – admittedly I haven’t found a great way to go from browsing another instance to beehaw’s “window” into that instance. I’ve been searching post titles from other instances while on beehaw and clicking in that way, but it’s not elegant. Hopefully other folks have better tips!