The entire process of manufacturing energy is known as oxidative phosphorylation, which takes place in the mitochondria, where ATP synthase enzyme is situated in the inner mitochondrial membrane and the F1-component protrudes into the mitochondrial matrix.
In the process, ADP combines with a phosphate to produce ATP. The energy liberated due to the hydrolysis of ATP into ADP is utilized to do cellular function, generally by coupling the exergonic reaction of the hydrolysis of ATP with the endergonic reactions.
The synthesis of ATP from ADP and Pi is an endergonic reaction with positive delta G.