What is an OTG cable and what is it used for?

An OTG Cable or On The Go adapter allows you to connect a full sized USB flash drive or USB A cable to your phone or tablet through the Lightning, Micro USB or USB-C charging port. It allows the transfer of data as well as connectivity to peripherals.

You can do the following with an OTG cable:

Plug in keyboards and mouse to the mobile
Access USB sticks and external hard drives ** (no need to store on device if using file manager to access)
Tansfer photos directly from a compatible camera on to the phone
Connect smartphone directly to printer