The first half of glycolysis is the preparatory phase. It starts off by adding a phosphate group to glucose (Glucose 6-phosphate). Next, the Glucose 6-phosphate is converted into Fructose 6-phosphate. Another phosphate group is added turning it into fructose -1,6- biphosphate. The fructose -1,6-biphosphate is then split in two, one part turning into G3P (Glyceraldehyde-3-phosphate) and dihydroxyacetone phosphate. The dihydroxyacetone phosphate is converted into G3P, leaving us with the two G3P triose sugar molecules used in the Pay-off phase.