Alarge boulder is balanced on top of a hill. you give the boulder a push, and it rolls down the hill. this is an example of converting energy to energy.

Potential energy to kinetic energy

Explanation:

Potential energy is the energy by virtue of its position

P.E = mgh

While

Kinetic energy is the energy by virtue of motion.

K.E = 0.5mv^2

At the top of the hill the boulder has maximum height and thereby possess maximum P.E, as it rolls down the hill the height reduces and velocity increases, so the P.E reduces and K.E increases(P.E is directly proportional to height while K.E is directly proportional to velocity). So as the boulder rolls down the hill its potential energy is converted to kinetic energy (according to the rule of conservation of energy).