Mechanism of ATP synthesis...is it a way to change carbohydrates into glucose?

No, carbs into glucose is DIGESTION. This is in the digestive system (obviously :-P) This takes place in the mouth (starch into maltose) and then in the ileum (maltose into glucose). It is then absorbed in the duodenum into the blood stream.

What you're refering to is RESPIRATION. Glucose and oxygen into ATP, water and carbon dioxide.

Glucose is absorbed into the cells out of the blood. In the cellular matrix it is broken down by glycolysis into 2 mmolecules of pyruvate and a net gain of 2 ATP and 2 NADH

The krebs cycle takes one pyruvate molecule and produces 1 GDP,  4 NADH and 3 CO2 molecules per cycle. Of course, as there are two pyruvate molecules made in glycolysis, this makes a net of 2 GDP, 8 NADH and 6 CO2.

BRB with oxidative phosphorilation...