Masturbation involves stimulation of one’s own genital organs to get pleasure, usually to the point of orgasm. In men, it usually involves stoking of penis using hands, although there are other ways of stimulation, such as lying with face down and rubbing the penis against the bed sheet or some other surface.
Masturbation in females, involves stroking or rubbing of clitoris using fingers, in some cases fingers are also inserted inside the vagina. Many a times, vibrators (dildo) are used for stimulation of clitoris and vagina.
Mutual masturbation involves partners stimulating each other. It is a common sexual practice.