There's links to video tutorials about adding songs to iPod here: How to transfer music to my iPod (& iTunes) {click on link}. There's two basic ways you can go about it. Sync your iTunes & iPod so all the playlists copy across. Else, use Manual updating which was my preferred way. That way you can select which songs you want to drag across.

But first you need to add the songs to iTunes music library if they are not already there. The link I gave shows the manual methods of adding music to iTunes.