The mitochondria is the cell's power plant . . . If each cell were compared to a city, every city would be under water. Each cell creates its own power in one of its many mitochondrion power plants. The red arrows point to some of the many mitochondrias found in each cell. With power, each cell can begin to act independently and self sufficiently, but they don't.
Cells work together because they want to.
Cells working together form organs, and organs working together form the human body. How this entire process takes place is unknown. We do know that blueprints exist on how all cells work together. Keeping with our analogy, each cell is a city, each organ is a state, and the many states make up a country. The country is one human being.