pinMode()
Configures the specified pin to behave either as an input or an output. pinMode(pin, mode) pin the number of the pin whose mode you wish to set mode INPUT, INPUT_PULLUP, OUTPUT none
void setup() {
pinMode(20, OUTPUT); // sets the digital pin as output
}
void loop() {
digitalWrite(20, HIGH); // sets the LED on
delay(1000); // waits for a second
digitalWrite(20, LOW); // sets the LED off
delay(1000); // waits for a second
}