OTG Micro USB Host Cable allows you to plug flash drives or other usb devices into your cell phone or tablet.

The use of the item doesnt allways require a rooted device, but the ability to use an OTG cable is if when your phones operating system was originally programmed in the factory, the kernel needs to have OTG USB support.  

Never the less, these cables are very handy for transfering pictures off your phone onto a usb memory stick, or watching movies on your device, or simple file transfering between devices.