Power chords are commonly heard from any hard rock and heavy metal bands. When these are played along with an overdrive or distortion effect the sound would be usually noisy and heavy. And because of their fretboard position, these enable you to move around the fret easily and quickly.
These are typically composed of two notes only: Root and the 5th note. Hence, they are indicated by writing "5" after the key like A5, E5, D5 and etc.
The above images are typical form of power chords where only two strings are played. However, to add more "power" to the sound, other guitar players also play the first high octave of the first note thus playing three strings at the same time. If you are playing F5 the finger position would be:
As you can see, 1st and 5th fingers are playing the same notes but the latter is one octave higher.
A great way of playing power chords is by damping. This is done by simply letting go of your grip a bit to the guitar neck while playing the chords. Also, palm muting is another way where you put your palm rested on the strings while playing the chords. This would definitely add bass or "heavy" effect on the sound. Do you hear the sound of Metallica or any other metal bands out there? If yes, then you hear the sound of power chords.