Array elements as counters

[abhishekphukan]

import java.util.Random;
public class apples {
 
    public static void main(String args[]){
        Random rand= new Random();
        int freq[]=new int[7];
 
        for(int roll=1;roll<1000;roll++){
            int index = 1+rand.nextInt(6);
            int f = freq[index];
            ++f;
            freq[index] = f;
        }
 
        System.out.println("Face \tFrequency");
 
        for(int face=1;face<freq.length;face++){
            System.out.println(face+"       "+freq[face]);
        }
    }
}

Please can someone explain the first (for loop)of the program...with an appropriate example will be really helpful.
Thank You.