Arduino 新手一問

買了Arduino Starter Kit
做到了project2__spaceship interface
請你們看一下code
我的問題是甚麼是int啊??
還有switchstate=digitalRead(2)的意義是甚麼?
都看不懂英文解釋
int switchstate = 0;

void setup() {

pinMode(3, OUTPUT);
pinMode(4, OUTPUT);
pinMode(5, OUTPUT);

pinMode(2, INPUT);
}

void loop() {

switchstate = digitalRead(2);

if (switchstate == LOW) {
digitalWrite(3, HIGH);
digitalWrite(4, LOW);
digitalWrite(5, LOW);
}

else {
digitalWrite(3, LOW);
digitalWrite(4, LOW);
digitalWrite(5, HIGH);

delay(250);
digitalWrite(4, HIGH);
digitalWrite(5, LOW);
delay(250);