Basically, how it works right now, you put the server name at the end of the community. So from a lemmy.ml account, browsing lemmy.ml, you can go to, say, https://lemmy.ml/c/socialism to go to a local community, and https://lemmy.ml/c/communism@lemmygrad.ml to go to a Lemmygrad community. Then you can subscribe, comment, vote, whatever.
How does that work? Do you have to sign in over on lemmygrad or do you have to search for the lemmygrad stuff via hex bear?
When that happens you should be able to find their communities under the communities tab, and view their posts when you view by all on the front page.
Basically, how it works right now, you put the server name at the end of the community. So from a lemmy.ml account, browsing lemmy.ml, you can go to, say, https://lemmy.ml/c/socialism to go to a local community, and https://lemmy.ml/c/communism@lemmygrad.ml to go to a Lemmygrad community. Then you can subscribe, comment, vote, whatever.