Plug your iPod touch into the computer, open iTunes and click on the iPod icon under "DEVICES" on the lieft side.
Now the window appears where you can tell iTunes which songs to sync. The easiest way is using playlists, e.g. you can make one playlist with all the Xmas songs and one smart playlist with the rules "playlist is music", "playlist is not Xmas songs". Important: tell iTunes if you want "any" or "all" rules to apply.
Then sync your iPod by clicking on the button down right. Hope this helps.