VSS: connected to ground
VDD: connected to a +5V power supply
VO: to adjust the contrast
RS: A register select pin that controls where in the LCDs memory you are writing data to. You can select either the data register, which holds what goes on the screen, or an instruction register, which is where the LCDs controller looks for instructions on what to do .
R/W: A Read/Write pin to select between reading and writing mode
E: An enabling pin that, when low-level energy is supplied, causes the LDC module to execute relevant instructions.
D0-D7: to read and write data
A and K: Pins that control the LCD backlight