@Senseibull
You can think of it like emails.
A lemmy community is like an automated mailbox that sends everything they receive to all subscribers.
You can host a mailing list/community on gmail.
Then you can subscribe to the mailing list from outlook.
Then a user can send a post to the mailing list from yahoo.
The automated mailbox at gmail will receive the message from yahoo and send it to outlook and all other subscribers.
@_finger_
We can have both generic instances and instances around a particular topic.
We already have a few lemmy dedicated to a particular community like latte.isnot.coffee and startrek.website