I have an older iPod Nano ( no idea generation) iTunes keeps asking to authorize my computer and I do but it still won't upload songs to iPod.

I have an older iPod Nano. Trying to upload music to it. iTunes keeps asking to authorize my computer. I do and try to sync but nothing is being synced. the iPod is connected and at the top of iTunes it states part 1 of 2 .... and the little wheeling thing is turning. Why is nothing being moved to the iPod? Help