Masturbation is defined as (I quote) "Exciting oneself by fingering your genitals". This is exactly what both sexes do to masturbate. Some women will actually stick a few fingers in, while others prefer a dildo or a vibrator. I've heard of a case where a cellphone was inserted and called. Anyway, try experimenting with what you like the most.
Generally it isn't anything like the way a man does it. Some women like penetration during masturbation, but most use a rhythmic rubbing of the clitoris. Usually with light pressure either in a circular or side to side motion.
Try Google and type in "Methods of masturbation for females."
Almost all female masturbation techniques will focus on stimulating the clitoris in a variety of ways until orgasm is reached. The best way to go about this task is to find a nice, quiet, private place, such as in a bedroom or where most men and women masturbate, the shower. If you're like me, you usually only resort to masturbation when you feel the need for some release of sexual tension, like when you're horny. Of course, masturbation just plain feels good, and doesn't depend on anyone else's ability to satisfy your needs, so often it is a great way to just let loose and relax. There are three main types of masturbation: manual stimulation involving the hands, water stimulation involving showers and jacuzzi jets, and auxiliary stimulation, involving dildos, vibrators, and other sexual toys. Part of the fun of masturbation is self-discovery.
There are many different techniques used to masturbate. You have to experiment for yourself to find out what works best for you. One way is to use your finger. Just explore. Another way is your bathtub! Position yourself under the tap so that your genitals are directly under the running water. Let the water continuously hit your clitoris. Some women swear by it!
Most often women masturbate by rubbing their clitoris similar to male masturbation but smaller. Often women enjoy the feeling of penetration at the same time. Some women enjoy only the penetration when masturbating but it's not as common as clitoral stimulation.
Masturbation is often done to satisfy a need, but it can also be refined to an erotic art in its own right. For many women, it is during masturbation that they experience their first Os (orgasms), have their first multiples, discover the G-spot and explore their innermost and possibly taboo fantasies. One good reason for experimenting with new things initially during masturbation is that you are in control and nobody else is involved or need know any details. There may be some kinds of sexual fantasies - especially the more audacious ones - that are best explored in the first instance in the privacy and comfort of masturbation. Take your time, start with your breasts (rather than the clitoris), fantasize and fantasize, and work your way down. Relax, wallow, enjoy, and O and O and O. Woman who masturbate can use all sorts of objects to masturbate with: hand, vibrator, cell phone* on vibrate mode, rubbing a stuffed animal between the legs, etc.).
*It is generally not recommended to use objects other than those designed especially for the purpose. Using household, or everyday, objects can be hazardous, especially because they are usually not sanitary, and they can also have sharp edges or points that can cause injury. Avoid these, or use with great caution.