A USB OTG adapter allows you to connect devices like keyboards, external USB hard drives, and even gaming controller to your Android smartphone or tablet computer.
USB Drives – When you plug in a USB drive, your Android will quickly display its contents. You can then play movies or music, view photos and open documents. The interface also lets you move or copy your data on the USB drive to your phone’s micro SD card. I found this to be the most practical use of the USB OTG adapter, and a quick way to transfer files onto your phone.

Keyboards – If you need to do some heavy writing on your smartphone for some reason, you could attach a standard computer keyboard, both wired and wireless, to type on your Android phone or tablet’s notes app. Even traditional shortcuts like Ctrl-C and Ctrl-A will work just fine.
Mouse – Now this is cool. You can connect a computer mouse, wired or wireless, and use a traditional cursor that pops up on the screen to navigate through your Android device.

USB Hubs – With a USB hub you can actually connect both your keyboard and mouse and use them at the same time. Using your USB OTG adapter, not only can you do this, but people will think that you have the world’s smallest desktop. Keep in mind however, that your Android device’s battery will drain pretty quickly.
Powered Hard Drives – Since your Android device charges whatever is connected to it, a self powered hard drive will not work. However, you can use a powered hard drive, since it relies on energy from an external source. And just like with USB drives, you can read, write and transfer files right onto your Android device.

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