Glycolysis is explained as simply as possible:

The glycolysis (Greek 'glykys' = sьЯ, 'lysis' = dissolution) is a part of the energy metabolism and found in almost all living things. Eukaryotes (plants, fungi, animals) and prokaryotes (archaea and bacteria) use glycolysis for the production of adenosine triphosphate (ATP), the universal energy source in the cell.
Due to the gradual breakdown of carbohydrates in the cell, four ATP molecules are formed during glycolysis. Since the splitting costs energy (two ATPs), the cell will gain two ATPs per glucose molecule as a result.
Advantages of glycolysis: The process is also possible in an oxygen-free environment. In addition, glycolysis is much faster than the citrate cycle. The latter is much more productive, but if the cell needs energy quickly, it can gain it from glycolysis.
Incidentally, the general formula for the breakdown of glucose looks like this:
C6H12O6 + 6 o2 6 CO2 + 6 H2O + ATP
Glucose + oxygen carbon dioxide + water + energy

Simplified flow of glycolysis

In ten steps, a glucose molecule is split into two pyruvates (pyruvic acid):
1. Phosphorylation: The glucose molecule receives an additional phosphate group (costs 1 ATP). The result is glucose-6-phosphate.
2. Isomerization: The enzyme phosphohexose isomerase converts the glucose-6-phosphate to fructose-6-phosphate (no ATP consumption!).
3. Phosphorylation 2: The enzyme phosphofructokinase phosphorylates under ATP consumption (costs 1 ATP) the fructose-6-phosphate to fructose-1,6-bisphosphate.
4. Splitting: The enzyme aldolase cleaves the fructose-1,6-bisphosphate into dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (GAP).
5. DHAP conversion: Another enzyme converts DHAP to GAP, leaving two identical glyceraldehyde-3-phosphate (GAP) present. From now on, all reactions are done twice.
6. CAP conversion: The enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) catalyzes the conversion of GAP to 1,3-bisphosphoglycerate (1,3BPG). At the same time there is a reduction of NAD + to NADH.
7. ATP profitThe 1,3-bisphosphoglycerate is now converted to 3-phosphoglycerate by the enzyme phosphoglycerate kinase (PGK). The enzyme causes the transfer of the phosphate group to ADP, which produces an ATP. As the reaction proceeds on two molecules, 2 ATPs are also formed).
8. Rearrangement: The enzyme phosphoglycerate mutase (PGM) converts 3-phosphoglycerate to 2-phosphoglycerate.
9. Creation of PEP: 2-Phosphoglycerate is converted to phosphoenolpyruvate (PEP) by the enzyme enolase.
10. ATP profit: The enzyme pyruvate kinase catalyzes the last reaction of PEP to pyruvate. The phosphate group is transferred by the enzyme to ADP, which causes ATP again (another 2 ATP).

Summary of glycolysis

4F-1,6-BPaldolaseDHAP & GAP
71,3BPG & 1,3BPGPGK3-PG & 3-PG+2
83-PG & 3-PGPGM2-PG & 2-PG
92-PG & 2-PGenolasePEP & PEP
10PEP & PEPpyruvate kinasePyruvate & pyruvate+2

Glucose-6-phosphate (Glu-6-P)
Fructose-6-phosphate (Fru-6-P)
Fructose-1,6-bisphosphate (F-1,6-BP)
Dihydroxyacetone phosphate (DHAP)
Glyceraldehyde-3-phosphate (GAP)
1,3-bisphosphoglycerate (1,3BPG)
3-phosphoglycerate (3-PG)
2-phosphoglycerate (2-PG)
Phosphoenolpyruvate (PEP)
Glucokinase (GCK)
Phosphohexose isomerase (GPI)
Phosphofructokinase 1 (PFK1)
Triosephosphate isomerase (TPI)
Phosphoglycerate kinase (PGK)
Phosphoglycerate mutase (PGM)