Chord names (or chord symbols) have two parts that stand side-by-side when we annotate them:
The root note (or the tonic) is the base of the chord. It's the note upon which all the chord's inherent intervals build.
The quality of the chord dictates which intervals are present in the chord.
So when we write a chord symbol, we define which intervals build upon which note by using the quality and the tonic, respectively. We thereby dictate exactly which notes must be played. Read more