Most times you'll want to listen to a song from start to finish, but if you want to locate and listen to a particular section, you can do it with the help of the little diamond location marker in the iTunes display."
While the song is playing, grab and hold the diamond pointer in the iTunes display and move it to the left or right to scrub through the song. The sound will be similar to rapidly flipping through a radio dial. Release the pointer to continue playing the song from the current point."
Scrubbing is the process of moving quickly forward or backward through a song as it plays.
You can do it on any media player - your iPod/iPhone, iTunes, Windows Media Player....whatever it is you use.
This DJ likes scrubbing too much.