In any key it is possible to build chords on each degree of the scale. This means that for every major scale there are seven possible chords which can be used for creating and harmonizing melodies.
These seven chords are called scale tone chords. It is common practice to describe all the chords within a key with roman numerals as shown in the following example which demonstrates the seven scale tone triads in the key of C major.
Here are the seven scale tone triads in C major played as arpeggios. The ascending pattern in bars 1 to 4 begins on the root of each new chord, while the descending pattern in bars 5 to 8 begins on the 5th of each new chord.
As always, learn them in the first position and then play them in all five forms of the major scale along the fretboard. Once you can do this in one key, play them in all keys; both around the key cycle and chromatically ascending and descending.