Kant has devised an ethic moral theory that he suggests people should live by. It is different from the utilitarian view because it is not based on emotion which Kant feels leaves to much room for injustice. His theory believes that if there is a moral rule that is in place, then it should always be followed.
His first formulation of the universal law states that one should act only according to the maxim by which you can at the same time will that it should become a universal law. In order to apply this formulation you would consider these three statements. The first question being, what rule would you be following if you were to perform this act? Meaning is there a moral rule that is already in place? Secondly, would a rational person want to universalize this rule? A person who is considered to be rational must know that difference between morally right and wrong and the difference in using a person with their knowledge and using a person without their knowledge. Once this is determined you have to decide whether the whole society should follow this rule. And thirdly, if you want to universalize the rule then the act is permissible. If you are not willing to universalize the rule then the act is morally impermissible. Therefore, once it is agreed that the rule is moral and justified by a rational person who feels that it should be universalized, it is allowed, and vice versa. .
An example of this would be: You are doing your taxes. You discover that you are required to pay much more than you had first calculated. Imagine that you are a tax expert and you know that you can falsify your records without getting caught (so that you pay the government less than is legally required). You decide to cheat on your taxes. .
If you were to falsify your tax records then you would be following the rule of lying. As a rational person you would not want to universalize this rule and allow lying to be accepted.