I subscribed to technology@beehaw.org, so I can see the posts from here. I did it by seeing a post from my local server (infosec.pub) and going to the community and joining it.
How do I get to other places in the Fediverse, though? I’m on jerboa and want to interact with e.g., https://kbin.social/m/asklemmy@lemmy.ml/t/11331/Is-Lemmy-your-first-time-on-the-Fediverse
If you put “!asklemmy@lemmy.ml” into the search (magnifying glass in the top right) then you’ll see a bunch of posts appear from that community.
Just above the list of search results is a link saying “<icon> asklemmy@lemmy.ml - 29 subscribers”. It is not very obvious or highlighted in any way. Lemmy should fix this.
Click on that and the contents of that community will be displayed - crucially, it’ll be displayed by your instance. You haven’t gone to lemmy.ml, you’re still on your home instance (check the address bar of your browser).
In the top right there is a nice big “Subscribe” button. Click it.