If you think about a scale as having eight notes – do re me fa so la ti do- and then assign numbers to the notes, you’d get one through 8, right? So your first note would be 1 and your last note would be 8 The one note is the “root” note in the scale and the other notes all different jobs to do when we play them as chords.
For instance a major chord has the scale notes 1, 3 and 5. For a C scale, which has no sharps or flats, the notes corresponding to the numbers 1 through 8 are C, D, E, F, G, A, B and C. So for our major C chord, 1,3 and 5 are the notes C, E and G. That makes a C major chord.
When you take the 3rd out though, something interesting happens. Playing the 1 and the 5 makes a very beefy, crunchy sort of chord, and playing a simple 1/4/5 pattern with that power chord is like the basis for tons of rock’n roll songs.
Conveniently for us as guitar players it doesn’t matter if you play the 5th note above or below the 1st note, and we have two strings in standard tuning, the D string and the G string that we can use to good effect for that. Consider: in the key of G (which has 1 sharp, the F#) the notes are:
G, A, B, C, D, E, F# and G Corresponding to 1, 2, 3, 4, 5, 6, 7, and 8
The cool thing is that the D and G strings are right next to one another!! So if you play them open, both at the same time you are actually playing the G (root) and the D (5th). Et Voila! G power chord.
Now if we want to play a 1/4/5 chord combination using power chords, we can do all that from the D and G strings just by holding the chord with 1 finger and moving it up the neck. Your open G and D strings will make a G per chord (also conveniently on the 12th fret where the two dots are, usually). Next, the 4th in the key of G ( a C chord) will be on the 5th fred of the G and D strings and the 5th will be a D power chord on the 7th fret.
The traditional turn around – 4, b5, 5 – you can do on the 5th fret, 6th fret and 7th fret.
All of this is by way of leading up to the fact that it you have a slide, you can make some reasonably decent slide-guitar noise right from the git-go if you lay your slide on those two strings and move it, keeping it more or less parallel to the neck of the guitar, between the 12th 5th and 7th frets.
Have some fun, turn up your gain a bit and you’ll see what all the fuss is about!