you can start with reading the manual which is written like a storybook. in-depth info of the 32 amps they model inside. they also have 12 effects built in for u to mix and match with the amp models.
for metallica stuff, try the "treadplate" model, based on the mesa boogie dual and triple rectifier.
for slash and rock stuff, dial in the " Brit J800" for the Marshall JCM800 and JCM 2000.
for jazz, try the " jazz clean". turn your settings all to 12 o'clock for a warm jazzy tone.
what i also like is the built-in compressor and noise gate.
for more info...go to www.line6.com. they even have a video demo.
if you have midi cables to spare, connect to the computer and go to www.customtone.com. it is a tone library whereby people round the world upload their tones for public sharing. you can download them. free. you'll be able to find your fav guitar player's tone there.