Is there a guide to do this for dummies? Subscribing is one thing, but is it possible to "comment" on another instance's community?

Edit: Figured out myself. It wasn't that difficult :) I agree with others that this needs to be mentioned more often. But, when I searched for "dotnet" in lemmy.world, it didn't return "https://kbin.social/m/dotnet" as one of the search results. Is this due to defederation? Is there a way to add a community using a unique identifier instead of searching for it?