sadeepa said:
But I wonder why it needs two inputs A & B? One input is more than enough.?
For most of the application you can do with one input, but two inputs gives you more flexibility. You can feed input data to Say input A and use input B as on/off switch. Thus when input B is high data on Input A will be shifted in, when input B is low Input A is disconnected. This can be very useful when you are planning to implement something without micro-controllers.