There are many chords. To read these charts, the fattest string (E) is on the left and the skinniest string (also E) is on the right. The top box is the first fret and the numbers are which finger and where to put it. Index finger is 1, middle is 2, ring is 4, and pinky is 4.
Power chords are where you put the first finger on one fret and the third finger 1 string down and two frets down the neck. You can strum these two strings anywhere on the neck except on the G and B string.