Java - No comprendo el for

package ejercicio14;

/**

 *

 * @author Francisco

 */

public class Ejercicio14 {

    /**

     * @param args the command line arguments

     */

    public static void main(String[] args) {

       int value = 0;

       for (int num = 10; num <= 40; num += 10){

       value = value + num;

       }

        System.out.println(value);

    }

   }

int value = 0;

for (int num = 10; num <= 40; num += 10) {

    System.out.println("-------");

    System.out.println("num: " + num);

    System.out.println("value: " + value);

    value = value + num;

    System.out.println("value: " + value);

    System.out.println("________");

}

System.out.println(value);

-------

num: 10

value: 0

value: 10

________

-------

num: 20

value: 10

value: 30

________

-------

num: 30

value: 30

value: 60

________

-------

num: 40

value: 60

value: 100

________

100