const int led = PB2; // pin -> LED -> GND
const int button = PB3; // pin -> button -> GND

void setup() {
  pinMode(button, INPUT_PULLUP); // tied HIGH
  pinMode(led, OUTPUT);
  digitalWrite(led, LOW); // turn LED pin off
}

void loop() {
  while (digitalRead(button)) // HIGH when button not pressed
    digitalWrite(led, LOW); // LED off
  digitalWrite(led, HIGH); // button pressed
}

/*
                                   +-- --+
         PCINT5/-RESET/ADC0/dW/PB5 |1 * 8| VCC
  PCINT3/XTAL1/CLKI/-OC1B/ADC3/PB3 |2   7| PB2/SCK/USCK/SCL/ADC1/T0/INT0/PCINT2
   PCINT4/XTAL2/CLKO/OC1B/ADC2/PB4 |3   6| PB1/MISO/DO/AIN1/OC0B/OC1A/PCINT1
                               GND |4   5| PB0/MOSI/DI/SDA/AIN0/OC0A/-OC1A/AREF/PCINT0
                                   +-----+
*/