As stupid as it may sound, I admit there are things about lemmy that I don’t understand. One of those things is the separation to .ml, .world and so on. I just came across a post on lemmy.world but it reads I haven’t logged in. So: do I have to create a new account in order to subscribe/comment on .world or can I use my current account from .ml?
If you’re using a browser and follow a direct link to a Lemmy post or comment in another instance, the link takes you to that other instance where you don’t have an account.
If you wish to interact with that thread by commenting, voting, etc., one easy way I’ve found to get to my local instance’s copy of that thread is to copy the URL of the other instance’s thread and search it using your own instance’s search menu. This will usually bring up the local copy of that thread as one of the top results. You can then interact with that thread through your instance with your existing account.
Links to communities have a mechanism that automatically translates the link to the local copy, which is to add an exclamation mark in front of the community address and then select the correct community in the inline search that comes up, which produces a link like this: !asklemmy@lemmy.ml
Unfortunately, I don’t believe that kind of mechanism exists for posts (threads) or comments yet, but perhaps it’s something that the developers will consider in the future.