Power chords are used by many artists because they are basically a chord which can be moved around almost anywhere on the fret board. Power chords are based on the root note and it's perfect fifth.

e|---------| B|---------| G|---------| D|----5----| A|----3----| E|---------|

In this example, the root note is C. In the scale of C, you have
C D E F G A B C. So now that you have the root note, you can find the perfect fith. The perfect fifth is the fifth note in the scale, so the perfect fifth of C is G (C D E F G A B C). So the power chord of C would consist of a C and a G. Sometimes the octave can be added. This makes the chord a little brighter. So you add another C an octave higher, so it would look like this...

e|---------| B|---------| G|----5----| D|----5----| A|----3----| E|---------|

So this is the power chord of C, however, it is usually refered to as C5. So if you wanted the F5 chord, it would be the power chord of F. You would have the root note, F, the perfect fifth, C, and the octave, F.

e|---------| B|---------| G|---------| D|----3----| A|----3----| E|----1----|

So all you have done is kept the same postion, but you have moved the chord so that F is the root note.

Now that you have learnt a bit about power chords, just try and practise moving the power chord up and down the fret board like this...

e|-------------------------------------------------|
B|-------------------------------------------------|
G|-------------------------------------------------|
D|-3-3-3-5-5-5-7-7-7-5-5-5-3-3-3-5-5-5-9-9-9-7-7-7-|
A|-3-3-3-5-5-5-7-7-7-5-5-5-3-3-3-5-5-5-9-9-9-7-7-7-|
E|-1-1-1-3-3-3-5-5-5-3-3-3-1-1-1-3-3-3-7-7-7-5-5-5-|

Listen

That exercise was only played on one string, so try these exercises on two stings...

e|-----------------------------|
B|-----------------------------|
G|----------3-3-----------6-6--|
D|--3-3-3-x-3-3-0-6-6-6-x-6-6--|
A|--3-3-3-x-1-1-0-6-6-6-x-4-4--|
E|--1-1-1-x-------4-4-4-x------|
Nirvana - Smells Like Teen Spirit

Listen

Saying that this position can be moved anywhere on the fret board is not 100% true. When you move the power chord so that the root note is on the 4th string, the position has to change to look like this...

e|---------|
B|----6----|
G|----5----|
D|----3----|
A|---------|
E|---------|

...And when the root note is on the 3rd string, the position must be like this...

e|----6----|
B|----6----|
G|----3----|
D|---------|
A|---------|
E|---------|

These two positions are rarely used by artists because:
· They are harder to play
· You can find all the notes you might want on the 5th and 6th strings.

And that is all you need to know about the basic power chord positions, but there are two main variations...

e|---------| B|---------| G|----5----| D|----5----| A|----3----| E|----3----|

This is basically the C5 chord, except the fifth has been added below the root note. This gives a fuller sound.

e|---------| B|---------| G|---------| D|---------| A|----3----| E|----3----|

This power chord has a root note and it's perfect fifth, however, the perfect fifth is played below the root note. This is known as an inverted power chord, because it is just an upside down power chord.