What we know — the motor.

Power in. Motion out.

A motor gets power. The motor spins.

Turn up the drive → generally faster.
Turn it down → generally slower.

Our example is a brushed DC motor, under the same load and within its operating limits. PWM lets us adjust the drive.

Wire it (+, −) → it spins one way.
Wire it (−, +) → it spins the other way.

What we know — the circuit

Current needs a complete path back to the power source.
In our DC circuit, that return is GND / supply negative.

With the polarity fixed, conventional current goes through the motor in one direction.

So, with the motor wired this way…

We can control its drive and speed.
But changing the power alone does not reverse its direction.

We need to swap the motor’s connections.