Red dot sight is a device that provides you with a red dot point that allows you to aim faster and more precisely. To install a red dot to your handgun, you need to have either an optic plate [for optics ready models] or a red dot mounts [for classic models]. There are many types of red dots sights, they differ in materials used, footprint used, the size and color of the dot, whether or not they have reticle, whether or not you can switch between the pictures for aiming, and other.