So USB OTG cable is used to connect to a device (say your phone, tablet) when you want to use that device (say your phone tablet) as a host. So imagine you want to use a mouse with your android tablet, then you can use the OTG cable as shown in the figure below
Major difference between the OTG cable and standard USB cable (or the uB USB cable)
In the uB or the regular cable, the ID pin would be left "floating" however in case of an OTG cable the ID pin would be connected to the GND. So that's how your device would know when to behave as a HOST and when to behave as a device
When you connect the regular USB cable to your device, it would see that the ID pin is floating and hence would work in Device mode.
When you connect the OTG cable to your device, it would see that the ID pin is grounded and hence would work in the host mode.
