Stage 1 of aerobic energy is Aerobic Glycolysis.

Glycolysis breaks down Glucogen which produces 2 molecules of ATP and lactic acid the ATP is used to keep that system working the ATP system lasts for 10 seconds. The lactic acid system lasts between 40-60 seconds and when this runs out your body will start to train much slower than before for example.

When you are doing press ups you can go at a really fast and powerful pace for 10 seconds which is the use of the ATP/PC system after this you will start too slow down and pain will start to kick in due to your muscles burning, this is because of the build up of lactic acid. The next stage of this is called the Kreb cycle.
The Kreb cycle is where everything going on reacts and then creates 2 ATP molecules, Carbon Dioxide is also created aswell as hydrogen.

The third step of the energy system is called the electric transport chain during this process the hydrogen that is created reacts with the oxygen that is created and creates 34 ATP molecules.