Help me in solving LOOPJ6V2 problem

My issue

i doesn’t understand this code

My code

/* package codechef; // don't place package name! */

import java.util.*;
import java.lang.*;

/* Name of the class has to be "Main" only if the class is public. */
class Codechef
	public static void main (String[] args) throws java.lang.Exception
		// your code goes here
		Scanner read = new Scanner(;
		int num = read.nextInt();
		int fact = 1;
		for(int a = 1; a<=num; a++)
		    fact = fact*a;

Learning course: Learn Java
Problem Link: CodeChef: Practical coding for everyone

This is the code to find the factorial of a number n.
like factorial of 4 -> 4*3*2*1=24;