Generally in English we use reflexive pronouns whenever the subject and the object are the same. For example we would say "he cuts himself" since the subject ("he") and the object ("himself") are the same. You would not say "he cut himself the hairs" because the object in that case is "the hairs" not him. You would say "he cut his hair". You would also not say "I cut himself" since again in this case the subject ("I") and the object ("himself") are different. You would just say "I cut him". There is another type of usage where reflexive pronouns are used to describe how something was done. For example you can say "I cut the hair myself", which means that I had no help in doing it. Its like a shorter version of "I cut the hair all by myself". You can use this with most verbs this way to explain that the subject was doing something on their own. Hope that helps!