I do not understand how I can use sum function to add 2+2. Could anyone explain that step by step? For instance 
package com.codegym.task.task01.task0128;

/*
As simple as 2+2
public class Solution {
    public static void main(String[] args) {
        int a = 2;
        int b = 2;
        int c = sum(a,b);//write your code here
    }

    public static void sum(int a, int b) {
        int c = a + b;
        System.out.print(c);
Why this won't work? What is the role of the last 3 lines that are given in this task? 
*/

public class Solution {
    public static void main(String[] args) {
        //write your code here
    }

    public static void sum(int a, int b) {
        int c = a + b;
        System.out.print(c);
    }
}
Many many thanks for insight!