a. Very first step,is that the substrate binds to the active site of the enzyme which fits into the active site

b. Then binding of the substrate will help the enzyme to alter its shape and size and will fit more tightly into it.

c.After that active site of the enzyme breaks the chemical bond of the substrate to form a new enzyme product.

d.And at last the product will be released by the enzymes in reaction and the free enzyme is ready to binding the substrate of another molecule and again run through the catalytic cycle.