Explain code

int pin1 = 9; 

int pin0 = 10; 

int pinSpeed1 = 11; 

int pin2 = 3; 

int pin3 = 5; 

int pinSpeed2 = 6; 

int analogPin = A4; 

int pin = 0; 

void setup() { 

// put your setup code here, to run once: 

pinMode(pin0, OUTPUT); 

pinMode(pin1, OUTPUT); 

pinMode(pin2, OUTPUT); 

pinMode(pin3, OUTPUT); 

pinMode (analogPin, INPUT); 

Serial.begin(9600); 

} 

void loop() { 

// put your main code here, to run repeatedly: 

pin = analogRead (analogPin); 

Serial.println (pin); 

if (pin >= 400){ 

digitalWrite (pin0, HIGH); 

digitalWrite (pin2, HIGH); 

digitalWrite (pin1, LOW); 

digitalWrite (pin3, LOW); 

analogWrite (pinSpeed1, 250); 

analogWrite (pinSpeed2, 250); 

} 

else if (pin <= 400) { 

digitalWrite (pin0, HIGH); 

digitalWrite (pin2, HIGH); 

digitalWrite (pin1, LOW); 

digitalWrite (pin3, LOW); 

analogWrite (pinSpeed1, 0); 

analogWrite (pinSpeed2, 0); 

} 

}