A sub oscillator adds weight
The sub is a simpler oscillator one or two octaves under Osc A. It follows Osc A's notes, so it thickens the low end without changing the tune.
A square sub is buzzy and solid. A sine sub is a pure, round weight you feel more than hear. Level brings it in.
Your turn. Add the Sub. The target has a soft, round low end under the saw.