What is the difference between energy and work done?

An object of mass $10 \mathrm{kg}$ is dropped from a height of $20 \mathrm{m}$. Calculate the potential energy and kinetic energy of the object at various heights as mentioned in the data:

Show by calculations that the above data verifies the law of conservation of energy. (take $\mathrm{g}=10 \mathrm{m}/{\mathrm{s}}^2$ )

Give reason for the following:

Winding the spring of a toy car makes it run on the ground.