The console.log() function is a fundamental tool for JavaScript developers. It's used to print messages or data to the browser's developer console or the terminal (if using Node.js).

Here's how you write a "Hello, World!" program:

console.log("Hello, World!");

When this code runs, the message "Hello, World!" will be displayed in the console.

You can log different types of data:

console.log("This is a string.");
console.log(123); // A number
console.log(true); // A boolean value
let myVariable = "Plenty of π";
console.log(myVariable); // The value of a variable