When you’re browsing music, you can rotate iPhone sideways to see your iTunes content in Cover Flow and browse your music by album artwork.

Drag or flick left or right.
Tap a cover or
.

Tap the track. Drag up or down to scroll through the tracks.
Tap the title bar. Or tap
again.
Tap
or
. You can also press the center button on the iPhone headset (or the equivalent button on your Bluetooth headset).