He starts off okay when he states
But from then on, I think he goes into the weeds when explaining horsepower.
Short explanation of power
Power is the speed at which the torque can be applied.
How much torque can we maintain on a spanner if the spanner is turning at 2000rpm?
On a stationary nut we can maintain say 50lbs/ft. But what torque can we maintain if the nut was turning at 20 rpm? The more torque we can apply to the spanner at higher rpm the higher the power. The same goes for an engine crankshaft. If we can maintain 200lbs/ft of torque at 9,000 RPM we will be making more power than an engine that can only put 100 lbs/ft of torque into the crankshaft at 9000rpm.
Increasing torque at 9000 RPM means we are using more power. The same torque at 2000rpm requires less power, less work, less energy.
When we know the torque number and the RPM, we can calculate/extrapolate the power being applied/used.
Its just that simple.
Torque is the force. Power is the rate at which we can apply that force.
StrikeEngine has a number of calculators related to power and torque
Measure engine power without a dyno