Some of that released energy causes the compost pile to heat. Besides energy, organisms need nutrients, which they also obtain from the feedstocks. In particular, they need nitrogen to build protein for cells and to reproduce. Generally, organisms need about one part of nitrogen for every 12 to 15 parts of carbon used, just for protein synthesis. Other nutrients including phosphorous and potassium are also necessary, but are not usually limiting.
Moisture is critical.
The microorganisms need moisture on the surface of all the particles as a medium to live and move in. But moisture also keeps nutrients in solution. The microbes can only use dissolved nutrients. For example, there should be enough moisture to keep ammonia in solution. If not, it becomes a gas, evaporates into the air, and the smell of ammonia is prevalent in your pile.