Easiest?
Use a nostr mobile app and save the mostr bridge relays in your relays.
Momostr.pink I think is another mostr bridge. But double check that one.
Something 'shit force' is another
Discussion
I use the mostr relay, it worked fairly well before. I've kind of forgot the following part...like go to mastodon then follow a newly generated account or something. It took me a while.
You mean their npub. For me it's easier to use a fediverse app like fedi lab, look them on there, copy their user address and enter it on nostr so they pop up