Here's a breakdown of how it works:

* ATP synthase is a complex enzyme found in the mitochondria (in eukaryotic cells) and the cell membrane (in prokaryotic cells).

* It utilizes the proton gradient (difference in proton concentration) across the membrane to drive the synthesis of ATP.

* Protons (H+) flow from an area of high concentration to low concentration through the ATP synthase, causing a rotation of the enzyme's components.

* This rotation powers the addition of a phosphate group to ADP, creating ATP.

This process is known as oxidative phosphorylation and is the primary way that cells produce ATP, the main energy currency of the body.