So if you have a metronome and are prepared to put in the time to do the exercises which Andy shows us you will build up a good steady rhythm that should serve you well across all styles. Remember what goes down must come up in order to go down again. As in down strokes and alternate picking.
4 to the bar is where you play rhythmic downs strokes on each quarter note and that's part of your familiarization with counting time and with your metronome you incrementally increase your speed after learning to count note durations with whole, half quarter and sixteenths notes. Take it slow keep it simple.
When you get to the part about triplets he explains that you need alternate picking D U D DDDDDD. Andy talks about all the techniques relevant to this style: pick angle, palm muting, dynamics and a lot more. There are practice tracks too.
If you want to jump right in to a style I heartily recommend this with the provisos mentioned above. Mind the neighbors!!! Get an amp with a headphone jack and practice on your own and others terms any time. This will teach exactly what it says: Metal. No Simon and Garfunkle here!
Metal Rhythm in 6 Weeks Page One | Page Two | Page Three
What’s money? A man is a success if he gets up in the morning and goes to bed at night and in between does what he wants to do. – Bob Dylan