You were told earlier in the thread about this and you chose to ignore it.
When a piece disappears from the sensor and amperes in a new position you assum it is the same pice being moved. So you update the array that holds the board position accordingly.
But it is a waste of time worrying about the hardware until you have an idea about how it is going to drive your software. What exactly do you want the finished project to do?
Is it to monitor a two player game or is it to act as an opponent?
Resistors are placed on the column or row pins of the matrix depending on how you wire it up.