The root note is the note that gives a chord its name and acts as its reference point. In a C major chord it is C, in Am it is A, and in G7 it is G. Because it shows the foundation of the chord, it is especially important when you are working out bass lines and chord progressions.
Reading the root from a chord name
In chord symbols, the note name written first is generally the root. In Cmaj7 it is C, and in Dm7 it is D. The part that follows, such as maj7 or m7, tells you which intervals are stacked on top of the root.
The relationship with the bass
The bass usually plays the root of the chord to support the foundation. Playing a low C under a C chord makes the center of the chord easy to hear. That said, there are situations where the bass plays something else, such as slash chords.
Thinking inside the key and the scale
Once the key and the scale are set, you can see the candidate chords built on each note as a root. The basic set of chords formed this way is the diatonic chords.
Inversions do not change the root
Even if you rearrange the notes of a chord so that a different note ends up lowest, the root that gives the chord its name does not change. A C chord made of C, E, and G still has C as its root when E is the lowest note. Knowing this lets you change the color of a chord while keeping its role.
How to check it in a DAW
Program a chord in the piano roll and try putting only the root note in a lower octave. Keeping the root in place while you change the other chord tones makes the foundation of the chord easy to hear.
