In this video is all the basic theory you'll need to understand why chords work and sound as they do. I'm focusing on guitar, but the theory remains the same for all instruments. Learn and enjoy.
open
Basic Open Chords
A Chord, by definition is a collection of several different notes played simultaneously. Open chords are ones which use an instrument’s open strings. Below are diagrams for the 8 most common open chords to get you started.
LTGuitarist 