This could be a topic of its own with its own right
In very simple terms (without using physics formulas and charts), power/BHP is the "work" the engine can do.
Torque is the actual turning force is can apply to the wheels.
So, in reality many believe that Torque is a better measure of how fast a car can accelerate and go, rather than BHP. Reasons are similar to what TNT mentioned. You might have 2 vehicles at 400 BHP each, but one weighs a lot more. The heavier one will not have the same acceleration as the lighter vehicle.
Another good analogy is arm-wrestling. Arm-wrestling is won by torque and not just power, because its the one who can apply the greatest turning force who wins.
Common saying: BHP sells cars, Torque wins races.