Adenosine Tri-Phosphate or ATP is often referred to as the "currency" of the body. Currency is any substance that is exchanged for goods and services. Much the same way as our typical dollar bill the cell uses ATP or the energy derived from ATP to make another molecule or protein do something in exchange for energy. ATP provides energy in order for them to perform a function that will contribute positively to the maintenance of homeostasis.
If you look at the diagram (in the attachment below) you will see that ATP is made up of ...
The role of ATP and how it provides energy and why it is critical to homeostasis.