Can I use my Beehaw account to log in to feddit.online? Or I have to make a new account?

Kay_Angel@beehaw.org to Beehaw Support@beehaw.org – 1 points –
5

The best way to interact with communities on remote instances is to first subscribe to them, so you can be sure your instance receives all content. The way to do this is to copy the community URL and pasting it in the search box of your instance. That should fetch it (if it wasn't already) and then you can subscribe.

You'd have to make a new account but why though? You ought to be able to subscribe to their communities with thus account. :)

what about communication / interaction? like replying on threads. is it possible with accounts from other lemmy instances?

Yes, as long as the two instances in question are federating with one another, then posts and comments are all federated.