Chords are 3 notes played at the same time. There are all types of chords. The most common chord is the major chord. Minor chords and Dominant 7th chords are used quite often as well. Some of them may have strange sounding names at first, but don’t let the name scare you.
Chord diagrams show you how to play new chords. This lesson (with video) will show you how how to read a chord diagram.