@junebug@mastodonbooks.net
Each server is independent, but they are connected together into a single network.
It's like with telephones: you use your phone provider's SIM card to make a call, even if the call is to someone on another phone provider, because it's your provider that lets you get onto the network.
Or email: if you have an account on Gmail and you want to send an email to a Yahoo address, you wouldn't try to sign in on Yahoo. You would sign in on Gmail and send the email to a Yahoo address.
@junebug@mastodonbooks.net
You don't need to log in on Journo.host to follow and interact with people from that server. For example, you and I are on different servers but we are having this conversation.
@feditips@mstdn.social @junebug@mastodonbooks.net not entirely true. If you want to see that server local timeline without restrictions, you'd need to have an account there. Otherwise from you server you only see (if you filter in Mastodon federated timeline or use Calckey's antennas) what others on it are following from the server you want.