Harmony is created when we perform two or more pitches at the same time. The term harmony also refers to chords in music and how those chords are related to one another.
A chord consists of three or more pitches played at the same time. The most common and most basic chord is the triad. Triads are chords made of three pitches, and they can be defined as major, minor, diminished, or augmented.
The correct pitches of a triad can be determined by using scale degrees and whole steps and half steps, in the same manor as major and minor scales. For a review of half steps and whole steps, visit that page in the section on Melody.
The triads have the following patterns of whole steps and half steps:
Major: W W H W
Minor: W H W W
Diminished: W H W H
Augmented: W W W W
Follow these links to determine the notes of triads and chords.
Summary of triads
Diatonic Chords, the Major Harmonic System, and Roman Numerals