You use himself to refer to a man, boy, or male animal.

In written English, himself is sometimes used to refer to a person without saying whether that person is a man or a woman. Some people dislike this use and prefer to use 'himself or herself' or 'themselves'.

In some religions, Himself is used to refer to God.

You use himself to emphasize the person or thing that you are referring to. Himself is sometimes used instead of 'him' as the object of a verb or preposition.