The basic Arduino Blink sketch is about as basic as you can get. It does not require any external components, nor does it require any foreknowledge of coding.

Here is the code, you can copy this or use the Blink example that is installed with your IDE. https://pastebin.com/3HFCUHqu

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/*

Blink

Turns an LED on for one second, then off for one second, repeatedly.

Most Arduinos have an on-board LED you can control. On the UNO, MEGA and ZERO
it is attached to digital pin 13, on MKR1000 on pin 6. LED_BUILTIN is set to
the correct LED pin independent of which board is used.
If you want to know what pin the on-board LED is connected to on your Arduino
model, check the Technical Specs of your board at:
https://www.arduino.cc/en/Main/Products

modified 8 May 2014
by Scott Fitzgerald
modified 2 Sep 2016
by Arturo Guadalupi
modified 8 Sep 2016
by Colby Newman
Randomized by AD0ND Dec 24 2017 http://www.mach1electronics.com

This example code is in the public domain.

http://www.arduino.cc/en/Tutorial/Blink
*/

// the setup function runs once when you press reset or power the board
void setup() {
// initialize digital pin LED_BUILTIN as an output.
pinMode(LED_BUILTIN, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
delay(random(250, 1000));                      // wait for a second
digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
delay(random(250, 1000));                    // wait for a second
}

Here is a short video of this code in action. https://youtu.be/HA-Xzcw0Bb8

Next: Expand on the Blink