As this is still a new server the communities you may want to join may not yet be shown on unilem.org. Use a site like lemmyverse to find your favourite communities. Copy the community id eg. [email protected] and paste in the search. Wait a few seconds and the community will pop up and you can subscribe. If you still need help DM me or reply in the comments.
Nothing I paste in the search seems to work. I've tried subscribing to Star Trek, Linux, KDE & Plasma Users, and Apple so far, and none of them work. It's possible I may be doing something wrong, as I'm not too familiar with the Lemmy system and how it works, having learned of its existence just half an hour ago.
Interesting update: after posting this, I was able to click on them like links and then subscribe. Still what am I doing wrong when I paste those in the search?
This is how I search.
Click on the search icon in the top right.
Then paste the community you want to search for in the [email protected] format. Once you click search wait a few seconds and it should come up. Mabye hit the search button a few more times if it doesn't but it should be there with 10 seconds or so.
Once that is done click on the community is the search results, and the community page should open. On the right you will see the community sidebar where you can subscribe