The power of Power Chords
"Nearly all men can stand adversity, but if you want to test a man's character, give him power."
- Abraham Lincoln

If you want a quick cheat sheet, go to the end of the post and download the cheat sheet.
Power Chords are the essence of rock n roll.
Yes, it's that plain simple.
Power Chords are chords that consist of only two intervals: the root and the 5th. They have no 3rd interval, so they are neither major nor minor.
You can play a power chord anywhere on the fretboard, but they are mostly played with the root note on the 6th and 5th strings, and sometimes on the 4th as well. It will look like this:

The root note is played in the thickest string, and if you know your fretboard well enough already, you'll be able to tell that the following note is a 5th interval.
The last note happens to be another root note, which is one octave higher. This note is optional; you don't need to play it, although in general I like how the chord sounds with it, so suit yourself.
Question: Did you notice that the pinky finger on the E5 is on the 5th fret instead of the 4th fret? Can you guess why?
The fingering I show in the diagram is the best in my opinion. Some people use their ring finger to form a small barre to press down on both strings like this:

This position is slightly easier as you use two fingers instead of three, but I recommend you avoid it as much as possible because in order to do that barre you often need to twist your finger in an unnatural way, the so-called "banana shape", like this:

This position might seem harmless, but it's actually very strenuous on your finger joint, and eventually it will cause pain, and from then onwards even worse consequences. Remember that no technique should cause pain.
We already know we call this mini-chords Power Chords, but how do we note them?
The usual way is to use the root note followed with a "5", such as "A5" for an A power chord, or "E5" for an E power chord. This notation makes it very clear that the chord is made up with the root note and the 5th interval.
Bonus!
If you are a rock fan, like I am, you can certainly think of a few songs right now where players play power chords very quickly. It is very difficult to play these shapes and change them very quickly, so how do they do it?
There is a small trick that works like a treat. Remember we talked about the third note being optional because it was another root note? Well, if they are both the same note, what stops you from playing one or the other? How about if you don't play the root note, but play the octave?
It would look like this:

In this way we can have a two-note chord that is easily playable with two fingers or even with a single finger (using a small barre), which allows you to quickly change positions, with the core of the power chord sound intact.

Notice on the photo above that the finger is not in the banana position. This will keep the health of the joint.
What we've done here is referred to as an Inversion of the power chord, which is defined as a change in the lowest note of a chord to another note other than the root. Don't worry, we'll see this later.
For quick reference, download the following infographic.
