How do I sync my IPOD to my (newly restored/ newly installed) ITUNES library/Account? Want to keep my Ipod songs and Transfer whats on IPOD to ITUNES..? HELP!?

I recently had to wipe my computer (PC), because of virus, etc destruction, so I'm reloading programs, etc. and now my newly reinstalled ITunes account is only reading I guess the initial library that I had when first using it, so many years ago...not reading purchases or updated playlists, etc...which ARE ON MY IPOD, (classic, 30G), and very importatn for me for work because I teach dance and need my music and playlists, etc. How can I sync my IPOD to my ITUNEs library without deleting or currupting all the music on my IPOD???! 😟 HELP! Never understood why Itunes is so tricky, and don't want to destroy my IPOD music...but need to transfer the music from my IPOD to my ITUNes library!..HELP?