First it may help to understand just what energy is.
Put simply, energy is the ability to perform work. Work is defined as the application of a force over a distance. If you apply a force to an object, and that object accelerates in response to that force, you have performed work. So you can say that energy is potential work. A bullet flying through the air has a lot of kinetic energy because it performs work, either the air through compression and friction, or upon the target and itself upon impact. Once it has lost all of its kinetic energy it simply sits there inert upon the ground or embedded in a target.
The concept of energy exists because it is much easier to understand physics and solve many problem if you think in terms of how much potential work an object can perform. It doesn't matter exactly how the object performs this work, it can only perform a set amount of work in a given circumstance. A bullet performs exactly the same amount of work whether it hits a target three feet away from the barrel or flies three miles before hitting the ground. So we say that the bullet has a certain amount of a quantity that we have labeled as 'energy' that can be converted or used in many different ways.
So in this way you can think of energy as 'bookkeeping'. We invent a quantity to help us with our physics and then we track that quantity as it gets converted to different forms and given to different objects. It exists simply because we have labeled this potential to perform work as an independent quantity itself.