Syncing music between Mac and iPod (old iPhone)

I use an old iPhone 4 as an iPod. I have a good number of Playlists on it. When I got a new computer last Spring (Mac Studio), I transferred my music from my old computer to the new computer (used my backup disc to move the music to new computer). However, all the Playlists were nowhere to be seen. I have read the Help topics regarding syncing -- still have questions and am confused. If I connect my iPod to the Mac Studio and sync Music library, does it only sync one way? Will what's on the Mac take precedence and I'll lose all those Playlists or can the Playlists on the iPod transfer to the Mac? I still have the old computer and all those playlists are still listed there. Is there a way I can get them over to the new computer if they won't transfer from the iPod? I've been hesitant to do anything because I don't want to lose those Playlists!