Glycolysis is a multi-step, enzymatic process which is common for both aerobic and anaerobic respirations. This takes place in the cytoplasm of the cell. There are as many as 10 steps in glycolysis and overall, 2 ATP molecules are used for one molecule of glucose.
First ATP is utilised when Glucose is phosphorylated to give rise to glucose-6-phosphate by the activity of the enzyme hexokinase and second in the conversion of fructose 6-phosphate to fructose 1, 6-bisphosphate.