Chords are made from notes from their respective scales. The first note of the scale is the tonic or root note. This is also known as the first degree of the scale. An interval , is any two notes played simultaneously.
Chords can be major, minor, diminished or augmented and colored with a sixth or seventh etc.
Most common chords in a key are built by stacking thirds on top of each other. Major or minor refers to the of the third of the chord. A major chord has two full tones between it's root and third, a minor has one and a half tones between it's root and third. A diminished fifth is flattened by half a tone and an augmented is raised half a tone. In the following table you can see how chords are built.