Subscribing to a community of another instance?

I'm sure this has been asked and answered before but I can't find it.

How do I subscribe to a community from another instance? I read you just search communities with the url of the community you want to join, but that didn't work for me. Even with variations in formatting: !community@instance, for example.

Perhaps there should be a sticky somewhere that explains the slight complexities of the fediverse since it's clearly a bit foreign to most users. I've been on lemmy for over a year and I'm constantly discovering functionality I was unaware of thanks to all the new lemons coming in and asking questions.