The electron-carrier proteins are arranged in the inner mitochondrial wall. A dehydrogenase enzyme (think of it as the first protein of the electron-transport chain) oxidises NADH2 (which is the reduced coenzyme NAD) and/or FADH2 (reduced coenzyme FAD). The energy from the oxidation process is used to pump hydrogen ions from the matrix to the inter-membrane space of the mitochondrion. Because of this, gradient of hydrogen ion concentration builds up across the inner mitochondrial membrane, which generates a potential difference across the membrane. The protons then flow back to the matrix through an enzyme called ATP synthase (also called ATPase). (This is called chemiosmosis because a chemical substance (H+) moves across a membrane, down the concentration gradient.) This releases energy needed for the ATP synthase to phosphorylate ADP, i.e. make ATP (chemical energy for use in the cell) from ADP and inorganic phosphate.
Note: Bolded things are important, everything else is just additional clarification in case you need it. This is the last major phase of cellular respiration. If you want a deeper insight into the process, I suggest you read a bit about glycolysis and Krebs cycle.
