All living things need a source of food. The food organisms take in provides them with energy,and also provides them with the resources and raw materials they need to build up their bodies, grow, and repair damage.
The foods that living things consume are very different depending on the life form. A cow eats a very different diet than a tiger. Even among humans, there is a great difference in what people eat around the world.
Plants use sunlight to create their own food.