There a four main types of piano chords. They are major, minor, augmented and diminished.
Major chords produce an untroubled, lighthearted sound. The are constructed of a major third on the bottom and a minor third on top. The most common beginners' major chord is C major, which consists of C, E and G.
Minor chords produce an angry or sad sound. They are also composed of a major and minor third, but in this case the minor third is on the bottom, and the major third is on top. An example of a minor chord is d minor, consisting of the notes D, F and A.
These chords are rare, and are typically used to lead from one chord to another. They are constructed of two major thirds. C, E and G-sharp is an easy example of an augmented chord.
Diminished is just the opposite of augmented. They are very dark sounding and consist of two minor thirds. B, D, and F make up a diminished chord.