Watch the Inversions online guitar lesson by Matthieu Brandt from Chord Cookbook
Three and Four note chords are mostly played with the root of the chord being the lowest sounding note; the bass note. The chord is said to be in 'root position'. The other notes of the chord are sometimes used as the bass. The reason for this is often to create smooth transitions from one chord to another in a progression. If a chord does not have the root in the bass (lowest sounding note) it is called an 'inversion'.