A vertical grip is an accessory that attaches to the bottom of a digital single lens reflex camera , usually in the tripod mount. The grip serves two main purposes.
The first is to store additional batteries to provide more power to the camera, allowing for an extended shooting time.
The second is to provide a more comfortable and secure way to hold the camera in a vertical position. Buttons placed on the grip duplicate the main controls of the camera such as the shutter release button. For the controls to work, the grip must be compatible with your camera.
Some grips also have small compartments for storage of remotes and memory cards. Some grips even enable WiFi communication with a computer.