The 3rd note of a chord is the bass note.
The 5th note of a chord is the bass note.
The small numbers attached just after a chord name means intervals between the bottom note and other chord tone. For example, In C6, 6 means the interval between the bass note E and the second note C in a basic voicing (from the bottom: E, G, C), but even the voicing order is not the basic way, the notation is same. It means X6 (or X6/3) always means a 1st inversion.
- Passing: It makes smooth bass line.
- Stationary: It is a kind of pedal point.
- Cadential: It behaves like dominant(V).