In our planet Earth, the Sun is the major source of energy. We need the heat of the sun to grow plants, which provide the food that we eat. The Sun also evaporates the water that falls as rain to water the plants. A baseball lying on the ground has potential energy, once somebody throws it the baseball's energy changes into kinetic. Energy is always changing back and forth from potential to kinetic.
Energy is measured in different ways.
When we feel cold, we like to rub our hands together, the faster that we rub them, the warmer that they get. This action is called friction. There is no such thing as a totally smooth surface. Even if they look smooth to the naked eyes, if we look at them through the microscope we will see that they have ridges and grooves. A vase on top of a table is an example of static friction.