Masturbation is a sexual act where a person ends up giving himself or herself pleasure to simulate actual sex. There are many different forms of masturbation out there, and some are enhanced with sex toys, viewers, adult movies, or other stimulants. Any form of manual pleasure a person brings to him/herself is considered masturbation.
Anyone can masturbate, even people with sex partners. Mutual masturbation is a common sexual activity couples try, which involves both people in the couple pleasing themselves at the same time. As long as you have even the tiniest sex drive, you can masturbate.
If you’re a guy wanting to masturbate, you can rub your hand up and down on the shaft of your penis to simulate the moving of a humping vaginal. If you’re a girl, you can either rub your finger in circles around your clitoris or you can stick them inside your vagina to finger your g-spot. There are tons of variants to these basic acts, but you can experiment on your own to build from that.