Wht is the purpose of undo option?

Programs that have an "Undo" option allow you to reverse actions you have taken on a file like the output file of a word processor, graphics editing program etc.. Some only allow the last step to be reversed and others allow a number of steps to be reversed. Many also offer a "Redo" option that lets you go back after you "Undo," If you change your mind again. Make a test file in the program you're using and experiment.