I haven't really figured morality out myself yet, but it stems from our ability to empathize with other people and organisms. Doing right by other people generally means helping them, while doing wrong generally means harming others. Obviously some harm can be done for the sake of a greater good and vice versa, but it's generally about the intent of the person doing the action. That's about the best explanation I can give at this point, as it's a pretty complicated subject.