Power chords are often used with distortion, but that's not what make them power chords...

Power chords are made up of just two notes, the root and 5th degree of the major scale. In the key of A an A power chord (written A5 of A (no3rd)) is made of the notes A and D.

As distortion is applied to and electric instrument, additional harmonics from each note are generated. the addition of more notes beyond the root and 5th tends to just make a sour mess..the two notes are more powerful then a soup of distortion. 

Power chords are easy to play. Here's some common ways to play and write power chords:

Here's the first two examples in a chord grid format:

Here's a larger power chord. Even though you are playing 4 notes they still are just the root (A) and the fifth(D) each note is doubled an octave highier to produce a fuller sound.