Data reduction is one the most important process of researches in astronomy and astrophysics. Data reduction includes all steps which convert the crude astronomical images to the astrophysical events. These steps are similar for different astronomical events in which the brightness of one star changes with time, although they may be different in some details. This paper will help for learning or even doing data reduction of each astronomical events. Data reduction of microlensing events contains 7 stages in which first the crude images will be calibrated. Then, some of the best calibrated images will be chosen for making the reference images. The reference image helps for comparing all taken images to indicate how the source light changes versus time. For this propose all images should be registered to the reference images. Then, all images should be taken to the same scale. Finally, the resulted images will be subtracted from the reference image, to find the light curve of the desired source star.
