Glycolysis is a 9-step process that breaks down glucose in the cytoplasm without oxygen. It requires 2 ATP molecules at the start but produces 4 ATP molecules and 2 pyruvate molecules at the end. Glycolysis involves many enzymes that catalyze reactions to break down glucose and other 6-carbon sugars into smaller 3-carbon molecules of pyruvate or lactate, with a net production of 2 ATP per glucose molecule.