From the top bar, click on Magazines. There should be search bar where you can search for lemmy communities/kbin magazines.
I searched for "canada" and there are many results of different Canada communities from different fediverse instances. Click subscribe on the right and you'll see posts in those communities appear in your sub feed.
@AndILearnedSomething Are you sure mls is on lemmy.world? I only see a mls@lemmy.ml community.
I went to lemmy.world and searched for the mls local community and I don't see it there.
https://lemmy.world/c/mls <-- doesn't work
Either way, you have the right idea, you put the community name after https://kbin.social/m/ , except without the !.
However when I tried https://kbin.social/m/mls@lemmy.ml it still didn't work while other communities like https://kbin.social/m/memes@lemmy.ml work. So I don't have a solid answer for you for why its not showing up in kbin. Perhaps someone else who's an expert can chime in. My hunch is that there's some slowness where kbin has not noticed there is a new mls community on lemmy.ml because of all the new people joining and its causing hiccups