GPIO - What is this/How this works..?

[zhendos]

Dear CPlusPlus community,

I have a RaspBerry PI 2B which I use pretty often.
I am still learning about the GPIO (General Purpose Input Output)
I wrote already my own C++ API for accessing the GPIO
(https://github.com/Xhendos/GPIO)

I want to continue to contribute on my API but get a little stuck.
On the way Python it does is the next:

(https://github.com/adafruit/Adafruit-Raspberry-Pi-Python-Code/blob/master/Adafruit_CharLCD/Adafruit_CharLCD.py)

# commands
LCD_CLEARDISPLAY = 0x01
LCD_RETURNHOME = 0x02
LCD_ENTRYMODESET = 0x04
LCD_DISPLAYCONTROL = 0x08
LCD_CURSORSHIFT = 0x10
LCD_FUNCTIONSET = 0x20
LCD_SETCGRAMADDR = 0x40
LCD_SETDDRAMADDR = 0x80

# flags for display entry mode
LCD_ENTRYRIGHT = 0x00
LCD_ENTRYLEFT = 0x02
LCD_ENTRYSHIFTINCREMENT = 0x01
LCD_ENTRYSHIFTDECREMENT = 0x00

# flags for display on/off control
LCD_DISPLAYON = 0x04
LCD_DISPLAYOFF = 0x00
LCD_CURSORON = 0x02
LCD_CURSOROFF = 0x00
LCD_BLINKON = 0x01
LCD_BLINKOFF = 0x00

# flags for display/cursor shift
LCD_DISPLAYMOVE = 0x08
LCD_CURSORMOVE = 0x00

# flags for display/cursor shift
LCD_DISPLAYMOVE = 0x08
LCD_CURSORMOVE = 0x00
LCD_MOVERIGHT = 0x04
LCD_MOVELEFT = 0x00

# flags for function set
LCD_8BITMODE = 0x10
LCD_4BITMODE = 0x00
LCD_2LINE = 0x08
LCD_1LINE = 0x00
LCD_5x10DOTS = 0x04
LCD_5x8DOTS = 0x00

Question 1: What are these 4 characters mean?

Also they use the next function to write via the kernel:

def write4bits(self, bits, char_mode=False):
""" Send command to LCD """
self.delayMicroseconds(1000) # 1000 microsecond sleep
bits = bin(bits)[2:].zfill(8)
self.GPIO.output(self.pin_rs, char_mode)
for pin in self.pins_db:
self.GPIO.output(pin, False)
for i in range(4):
if bits[i] == "1":
self.GPIO.output(self.pins_db[::-1][i], True)
self.pulseEnable()
for pin in self.pins_db:
self.GPIO.output(pin, False)
for i in range(4, 8):
if bits[i] == "1":
self.GPIO.output(self.pins_db[::-1][i-4], True)
self.pulseEnable()

Question 2: How does this method exactly work?

I hope someone could answer my question so I can contribute on my own API and understand what to do and on which way I could do this.

Thanks!