Energy transfer describes energy in some form, usually heat or electricity, being transferred from one object or substance to another. There are natural examples of energy transfer like the sun heating up land, and also manmade examples of energy transfer, such as an oven cooking food with heat.
There are many forms that energy can exist in, including sound, heat, light, nuclear and kinetic. Some forms are more abundant than others and contain more energy. Since energy cannot be destroyed or created, it can only be transferred. It can, and is often transferred from one source of energy to more than one different forms of energy. For example, when a candle is burnt, energy is given off in the form of heat and light.
Not all energy takes on a moving form. In the above example, a candle possesses chemical potential energy, even when not lit. When lit with a flame, there is a chemical reaction that releases energy. Similar to chemical potential energy, an object can also have physical or elastic potential energy. Energy can be stored in these forms in items until a force acts upon it. A person falling from the sky has physical potential energy that is being lost as gravity acts upon them.