Inside the main program, there are two blocks namely void setup () and void loop () statement. One that will only be executed once when starting the program and another part in which an infinite loop will be generated.
The void setup () is usually used to initiate serial, i2c, isp, etc. communications, to declare the function of the terminals of the Arduino board: inputs or outputs, and also this instructions block can be used to assign predefined values to variables.
The infinite loop which is found from void loop () encompasses the program that will run on the microcontroller of the Arduino board.
We can also see that each group of blocks is between 2 braces that delimit them, that each sentence ends with a semicolon and that comments can be added to the program without affecting it by adding 2 sidebars.The LED_BUILTIN indicates PIN 13. Inside the void loop () the LED will be switched ON and Switched OFF with a delay of 1 second using instruction digitalWrite(pin_number, HIGH) and digitalWrite(pin_number, LOW).