Here is a brief way or breaking this all down. Hopefully this makes sense. :)

All western music starts with the major scale. The scale is made up of seven notes, and those seven notes each have a tonality and value that allows you to build a chord from each note. We will use C major, and here are the values for each chord in the scale.

C - major
D - minor
E - minor
F - major
G - major
A - minor
B - diminished

These are all based on triads for each scale degree. You can play all these chords in any order and in whatever way you wish and the tonality will still be in C major. Each scale degree has a tonality as I stated that is either major, minor, or diminished.

Cool?