Energy is what fuels any system for work. This includes living and non-living matter. As an example, energy within a human gives us the ability to walk, talk, and even eat food, while the sun's energy is used for providing the Earth and other planets in the solar system with atmospheres.
Energy is a vital source of life, and without it we simply wouldn't exist. Energy can take on multiple forms. And some metahumans have the ability to manipulate it. This super power is called Energy Manipulation, which can be used in a variety of ways, such as the creation of Energy Constructs, and the ability to absorb, negate, transfer and even project energy. People with the ability to project energy, such as Darkseid, who uses the Omega Effect, are able to project deadly bolts of energy.
Although energy is necessary, too much of it can be lethal. Radiation is an excellent example of this. Another example of harmful energy is heat, which can be deadly if the temperature rises too high. Similar is the aforementioned Omega Beams, which are deadly to most beings that are blasted with them. Even Superman cannot completely withstand such awesome energy, however, once when he was near the edge of the sun, his super powers were super-charged, and when he faced Darkseid, he was able to withstand the energy of his Omega beams, without it even harming him at all!
However, energy from a yellow sun may be good for a Kryptonian, but too much energy is still not good for all people, at least not humans. One human, named Icy Harris was attempting to drain all of Superman's energy, but he didn't realize his fragile human body couldn't take so much energy and he exploded due to being overloaded.