Heat is a Form of Energy
All forms of matter, from a cold slab of marble to your own skin, have some temperature. Different materials conduct heat in different ways, but heat will always flow from the hotter material to the colder material. Take the example of an aluminum can and a Styrofoam cup. Your body temperature is hotter (usually) than both of those objects. If you hold one in each hand the heat from your hands transfers to the can and the cup. Because aluminum conducts heat better it will transfer the heat throughout the can. Styrofoam is not a good conductor, so the heat stays mainly where your hand is touching the cup. The can feels cooler, but that is only because the heat has been transferred to the entire can.
How Heat is Produced
Heat is produced when molecules bump into each other and transfer the heat. A conductor like the aluminum can transfers heat quickly. Styrofoam is an insulator and conducts heat more slowly. The contrary is also true. Styrofoam makes an excellent cooler because it takes longer for the heat outside the cooler to spread inside. Conduction is the transfer of heat to different objects, such as from a hot iron to clothing. Convection is the transfer of heat by the movement of air or fluids. For example, a convection oven uses circulating air to heat the oven quicker and more evenly. Radiation is the transfer of heat waves through space as in solar rays or a heat lamp.
Heat can be created in many ways, but the most basic, natural form is solar heat. Solar energy is just that; heat produced by the sun and absorbed by other materials. Dark-colored objects absorb light and heat faster than light-colored objects. Dark objects also store heat longer. Light-colored objects appear lighter because they are reflecting most of the solar heat away rather than absorbing it. For this reason solar panels used to create electricity are black.