Glucose is a simple sugar that contains chemical energy. Oxidation of glucose provides the energy the cell needs to live. When glycolysis occurs, glucose is converted to pyruvate. This is part of a metabolic pathway. Free energy that is released is converted into adenosine triphosphate also known as ATP. ATP is a type of "energy currency" that cells use to carry out life processes. The process of glycolysis occurs in the cytosol of cells. Glycolysis occurs in organisms that carry out anaerobic, as well as aerobic respiration. The second link below provides an animated view of glycolysis that is very helpful.
Glycolysis is a catabolic reaction involving the breakdown of glucose into 2 pyruvic acids, 4 ATP's, and NADH+ molecules. This reaction is anaerobic and occurs throughout the cytosol.
Glycolysis is an enzyme mediated reaction that allows the majority of stored energy of the glucose molecule to remain in the pyruvates. In fact, C6H12O6 becomes (2) C3H4O3 molecules. The only thing lost through this process are 4 H+ ions.