This is glucose and he is about to be converted into energy in a process called Cellular Respiration.
Glucose gets broken down in the cytoplasm, it gets transformed into 2 ATP and 2 pyruvate acid. NAD+ is converted in NADH. This process is called glycosis.
This next process is called Kreb's Cycle. In this stage the pyruvate acid gets transferred into the mitochondria where it loses Carbon dioxide to form acetyl-CoA(red block).
acetyl-CoA then gets oxidized and releases NADH(Yellow) FADH2(Green) and ATP(Teal)
The last process is called the electron transport chain. In this process NADH and FADH2 enter the cytoplam and undergo changes. As electrons pass down the chain they go from high to low energy because they are pumping H+ ions through the matrix into the intermembrane.
Here at the end of the transport oxygen molecules are transferred electrons which use H+ to create water.