The animal life forms are characterized by their inability to absorb light energy from sunlight, although these definitions are simplified. Vegetable life forms are generally rooted in one place, whereas animal life forms are generally capable of movement. A mushroom is rooted in one place; although it does not absorb sunlight for energy, it relies instead on the energy content of its food. In recent years, the scientists who classify things have decided that fungi are different enough from plants that they should get a third, separate category. Life forms now are "animal" and "vegetable" life forms, some of which are called "plants" and some called "fungi."
The ultimate source of life energy is sunlight. Many life forms take that energy, store most of it in their physical and chemical structures, and use up the remainder. Those life forms are plants, and they are eaten (while alive) by animals, and sometimes by fungi. Some of those animals are eaten by other animals. Some of the plants and animals that were lucky to not be eaten entirely by others eventually die. Various fungi and plants and animals feed on the corpses. Various other fungi and plants and animals feed on them. Generally speaking, the ones that move the fastest and/or grow the fastest and/or multiply the fastest tend to survive. For example, fast-growing plants that scatter many seeds flourish in the Amazon rain forest, even though they cannot run quickly. Humans move quickly, even though they do not grow the fastest nor multiply the fastest. The life span of an individual life form is also obviously a factor. Every life form has some factors that combine to favor its survival.