Probably the most well known sex toys are 'vibrators' which, as the name suggests, provide stimulation of the genitals using vibration. They are mainly used to stimulate the clitoris, but may also be used to stimulate any other part of the female body or that of a man's.
The simplest of these are pencil or wand shaped (though normally thicker than a pencil). They often have an internal battery (or two) which powers a small electric motor. Sometimes the battery pack and controller are external and connected to the vibrator by a wire. This motor is fitted with a small, out of balance, weight attached to the shaft. As this weight rotates it throws the motor and vibrator into a small circular movement which causes the vibration you feel.
With a vibrator that has a controller, as the power is increased the speed of the motor increases and with it both the rate and strength of vibration. Both the strength and rate of vibration effects how stimulating you find the sex toy. The best effect may not be as strong and as fast as possible. The optimum settings may well change as your degree of excitement builds. To get the best results it is worth buying a vibrator which is controllable.
Different vibrators will have different characteristics and you may well find you prefer one combination much more than another and your preference may even vary depending on which part of your body you are stimulating.
More recently electronic vibrator controllers have appeared which provide not only the static control of power/speed but also allow you to select patterns of power pulses and surges. These can be very effective.
There are also other vibrating sex toys such as butterfly stimulators and vibrating penis rings.