Can anyone explain this?

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ImageShack.us#include <LiquidCrystal.h>
const int timerstart = 8;
const int timerstop = 9;
int seconds = 0;
int timerstart1 = 0;
int timerstop1 = 0;
int output = 13;
int setseconds = 10;
int on = 0;
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
void setup() {
lcd.begin(16, 2);
pinMode(timerstart, INPUT);
pinMode(timerstop, INPUT);
pinMode(output, OUTPUT);
seconds = setseconds;
}
void loop() {
timerstart1 = digitalRead(timerstart);
lcd.setCursor(0, 0);
lcd.print("Time: ");
lcd.println(seconds);
if (timerstart1 == HIGH) {
on = 1;
}
if (timerstop1 == HIGH) {
on = 0;
}
if (on == 1){
seconds--;
delay(1000);
}
if (seconds == -1) {
digitalWrite(output, HIGH);
seconds = setseconds;
on = 0;
delay(1000);
digitalWrite(output, LOW);
}
}