

Both services use the ActivityPub protocol, so to put it very simply the data format used by both services is the same, they just render it differently on your screen. Then they are pushing/pulling the data for posts and comments from other instances as users request it, e.g. by viewing this lemmy instance through Mastodon.
Maybe slightly off-topic, but how did you end up with the name “reitti”? You say you’re German - do you have some sort of tie to the Finnish language?