If the desired community on a remote instance is not already available on your home server, then you have to paste the URL (e.g. https://lemmy.helvetet.eu/c/sverige) to the search field. Your server will then fetch the community and it should appear after a couple of seconds!
Thanks for the info here, I was experiencing a similar issue and I wasn't sure if I was doing something wrong. With this being the case (server not showing results until someone has already linked the servers by subscribing, if I'm understanding that right) is there a good or best-practices way for users to discover new communities across the Lemmy platform? Or should we just trawl through the different servers?
In addition, I've joined a couple of communities from other servers, but I only seem to be seeing a very small subset of their posts, is this again just from my server not yet being linked and maybe needing time to propagate the data?