Make an external LED blink
Arduino Uno
Breadboard
LED
200 Ω resistor
Wires
To connect a LED to the Arduino board, the shorter leg must be connected to a ground pin. The longer leg must be connected to the digital pin, but it must have a 200 Ω resistor in between. The resistor is required to avoid the LED to get to much current.
Then just code as in the SOS signal lesson.