You can assign a rating to a song (from 1 to 5 stars) to indicate how much you like it.
You can use a song rating to help you create Smart Playlists automatically in iTunes.
To rate a song:
Start playing the song.
From the Now Playing screen, press the Center button until the five Rating bullets appear.
Use the Click Wheel to assign a rating (represented by stars).
The ratings you assign to songs on iPod classic are transferred to iTunes when you sync.
Note: You cannot assign ratings to video podcasts.