Any sex toys that are designed to penetrate and are firm enough so they will not bend can be used for stimulating the G Spot. However sex toys with a bent tip are designed as a G Spot vibrator. This bent tip makes it easier to apply the pressure needed to stimulate the G Spot area. As will most sex toys these vibrators come in a range of textures and functions from basic single speed to multi speed and random pulsing.
How to use
First keep in mind that everyone's body is different so you may not get it right first go. With your sex toy angled up and facing your belly button is the correct way. Insert into the vagina about 2 or 3 inches. While stroking in and out apply pressure on the out stroke. If you get a sensation like you want to pee don't worry this is a signal you are doing it right.