This song is in drop D tuning. In drop D tuning the low E string is
tuned down one whole step to D. This enables the guitarist to play power
chords with a single finger. If your favorite band uses drop D tuning
and you want to experiment with this tuning, by all means do so. What
ever you do, don't learn the guitar in drop D tuning-you'll get all
mixed up.
To tune your guitar to drop D tuning, first make sure your tuned to
standard tuning. Then you'll want to tune your low E string down two
steps to D (we drop it down one step, hence the name). See the picture
below. You can use the audio clip below to tune your low E string to
D for drop D tuning.
I'm picking this riff finger style, but you can use a pick
to play it too.