Follow torque and rpm from the pistons to the tire contact patch. Set the throttle and pick a gear, then watch what reaches the road and what pushes back.
The pedal controls how much air and fuel each cylinder gets, which sets how hard each piston is pushed. At any given rpm, more throttle means more torque at the crank.
Torque is how hard the crank twists. Power is how fast that twist does work. The same torque at twice the rpm is twice the power. In US units, hp = lb·ft × rpm ÷ 5,252.
A gear pair cannot create power. It divides rpm by its ratio and multiplies torque by the same ratio. First gear hands the wheels about 14.5 times the engine's torque at 1/14.5 of its speed. Sixth hands them about 2.6 times.
The tires push with wheel torque ÷ tire radius. Air drag grows with the square of speed, so the power needed to beat it grows with the cube. Whatever push is left after drag, rolling resistance and grade accelerates the car. When nothing is left, speed holds.