With 500 ms on and 500 ms off, a full blink takes one second. Delays set the rhythm; wiring and a series resistor matter when you build the real LED circuit.
Follow the current path
The external LED lesson uses D13, a series resistor and an LED returning to GND. The resistor limits current. An LED has polarity, so reversing it can prevent it from lighting. In the browser, open the Connections panel and identify both connections before running the sketch.
Understand the two parts of a sketch
setup() runs once after startup or reset. pinMode(13, OUTPUT) configures the pin to drive an output. loop() repeats: write HIGH, wait, write LOW, wait. A delay value is measured in milliseconds. With 500 ms on and 500 ms off, a complete cycle takes about one second.
Make a prediction and test it
Open lesson 2, press Run and watch the LED. Change only the on-time from 500 ms to 1000 ms, leaving the off-time at 500 ms. Predict a longer illuminated phase and a 1.5 second cycle, then compare the result. The serial monitor helps connect pin states to what you see.
Before using real hardware
Disconnect power before changing wiring. Keep a series resistor in the LED path, verify the LED polarity and share GND with the board. Use the official Blink example in Arduino IDE for a real board; the learning app’s Run button does not upload to USB hardware. Never treat a maximum current rating as a normal operating target.
Go beyond the experiment
Check the primary sources
Use official board documentation and component datasheets to check physical wiring and specifications.