How do I sync music from my ipod to Itunes?

I have Itunes on my computer but then it got a virus and then I had to take it for repair. They said the hard-something was broken so they changed everything and added a new one. Now I got it back its just like a brand-new computer. I downloaded Itunes yesterday and I dont feel like downloading the songs again one by one, so I want to connect the ipod to the computer but I dont know how to do that. Because last time I did it on my old computer I connected and it said something like this :this ipod is synced to another Itunes library, would you like to sync the ipod with this itunes and it deleted all my songs from my ipod.

What should I do? Could you put like step by step?

Thanks in advance!