Thank you all. I appreciate your help. I get it now.
So the ^ shaped pin on the left is not a pin... The pin connected to a filled cylinder is ground and the rest two pins are connected together unless the jack is connected to wall socket. Right?
And I need not worry about the pin in the middle as it is irrelevant at the moment. However the pin connected to the ^ shape is +ve...
But I do get the concept of the pin in the middle. It is meant for an alternative power source, right? It is there just in case I needed to connect a battery for the time when the jack is NOT connected to the wall socket. When the jack IS connected to wall socket, the battery will be disconnected from the circuit (and the power coming from power adapter will not be charging the battery)...
At least that is what I gather from all your comments... I can proceed to use the symbol in my schematic... Thanks again, everyone.