How memory Card Works in your devices ? what is principle of operation?

Above picture shows the pin out of a memory card which we use in our digital devices. here is a short points about the concept of memory card.
Pin no 1- named as DATA2 but it sends data signal 1
pin no 2- named as DATA3 but it sends data signal 2
pin no 3- CMD I/O means sends commands for Input and output .
pin no 4- named as GND and supplies ground or negative voltage to this component.
pin no 5-named as VDD and supplies positive voltage to this component
pin no 6- Named as CLK and provides clock signal to card to execute the instruction to the card for output
pin no 7- named as GND and supplies negative voltage
pin no 8- Named as DATA0 and provides path for data signal 0
pin no 9- Named as DATA1 and provides path for the Data singal 1