This stored energy gets converted to kinetic energy as you fall. When you jump from the top of a building, the stored energy gets converted to so much kinetic energy, in fact, that your legs can no longer brace against the collision. Energy can be stored in a spring. The potential energy of a spring depends on what the spring is made of and how far back the spring is pulled. The stiffer the spring, the more energy can be stored, and the further it is pulled back, the more energy is stored.
Potential energy is stored energy.
If a spring is made of a material which is very stiff, then it will have more potential energy than a spring made of a material which is less stiff. If two springs are pulled back the same amount, but one is made of a material which is stiffer than the other, then when the springs are released, the spring made of the stiffer material will recoil with more energy. Secondly, if a spring is pulled back really far, it will have more energy than if it is pulled back just a little bit. We know this because when we release a spring which has been pulled back really far, it recoils with more energy than a spring which is just pulled back a little bit. A moving object has energy known as kinetic energy.