The shared 'Kim's Frostwire Tunes' in iTunes is just a playlist. It doesn't contain the music files themselves & so you can't transfer files from there

In FW's library, highlight a file & then click Explore...your saved folder should open. Transfer to the iTunes library from this folder & then you'll be able to transfer files to your iPod.

There's a lot more info here. It's referring to LimeWire, but same goes for FW.
Transferring music to iPod & iTunes