Your first class and the main method

The entry point every Java program needs.

The shape of a program

Every line of Java lives inside a class. Execution starts at a special method called main, which the JVM looks for and calls. Its signature is fixed — memorise it:

public class Hello {
    public static void main(String[] args) {
        System.out.println("Hello, world!");
    }
}

Reading it piece by piece:

public class Hello — declares a class named Hello. A public class must live in a file of the same name: Hello.java.
public static void main(String[] args) — the entry point. public so the JVM can call it, static so it runs without creating an object, void because it returns nothing, and String[] args receives command-line arguments.
System.out.println(...) — prints a line to standard output.

Every statement ends with a semicolon; blocks are wrapped in { }.