Forgive me if this explanation is VERY geeky. I am a retired electrical engineer who specialized in motors and motor controls. Torque vs speed was my life for MANY years. I will try to explain it for non-geeks.

Torque is the number that REALLY matters. I think it was Carol Shelby who said "Horsepower sells cars but torque wins races." Torque is a force times the length of a moment arm. If I turn a wrench with a given amount of force, the torque applied to the bolt is the force multiplied by the length of the wrench. If I use a wrench that is twice as long and apply the same force, twice the torque is applied to the bolt. The units for torque are pound-feet, also said foot-pounds. This is pounds multiplied by the moment arm in feet. (Newton meters for metric lovers).

Power is torque multiplied by the rotational speed.

A dynamometer measures the torque produced at a given speed. Then it changes the speed and measures how much torque is produced at THAT speed. Then it changes the speed and again measures the torque produced. The result is a chart that shows the torque produced at each speed. Then power is calculated for each speed by multiplying the torque produced at that speed times the speed. The result is then shown as a power vs speed chart.

At a given speed, the torque produced by the engine is multiplied by the gear ratio of all of the gears between the engine and the wheels. For example, if the engine is producing 300 ft pounds of torque and the car is in first gear (2.65:1) then there is 795-foot pounds of torque coming out of the transmission (300 times 2.65). Then the rear end gears multiply it again. If the rear end is a 3.23:1, then there is 2568 foot pounds of torque being applied to the rear wheels (795 times 3.23). A 205/75R14 has a diameter of 26.1" (call it 26") This gives us a radius of 13" or 1.08 feet (13/12=1.08) 2568 foot pounds divided by 1.08feet = 2377 pounds of thrust applied by the wheels to the pavement. Sir Isaac Newton says that acceleration is force divided by mass. The actual equation is given as F=ma. Algebra gives is a=F/m. This means that the thrust applied to the pavement by the wheels directly causes acceleration.

The thing that is misleading about showing the horsepower for an engine or motor is that since power is torque multiplied by speed, you can get high power with very little torque if you spin it fast enough. Because in this case, the torque produced is low, so is acceleration.