As we know from the law of conservation of energy: energy is always conserved.
Work is the product of force and the distance over which it moves. Imagine you are pushing a heavy box across the room. The further you move the more work you do! If W is work, F the force and x the distance then.
W = Fx
Energy comes in many shapes. The ones we see over here are kinetic energy (KE) and potential energy (PE)
Transitional KE = ½ mv2
Rotational KE = ½ Iw2
here I is the moment of inertia of the object (a simple manner in which one can understand moment of inertia is to consider it to be similar to mass in transitional KE) a w is angular velocity
Gravitational PE = mgh
where h is the height of the object
Elastic PE = ½k L 2
where k is the spring constant ( it gives how much a spring will stretch for a unit force) and L is the length of the spring. Simple isn't it!!