The simplest way is as follows. from the iTunes Help files:
To load songs onto iPod manually:
Connect your iPod to your computer.
When the iPod icon appears in the iTunes window (under Devices), select it.
If the Summary pane is not showing, click the Summary tab.
Select "Manually manage music." (If you have an iPod that displays video, the checkbox says "Manually manage music and video.")
Click Music (below Library, on the left side of the iTunes window) and then drag songs and playlists to your iPod.
...I guess I didn't look hard enough
in the Help file!! ;-)
Thanks!