Please explain the next steps
import java.util.*;
public class Main {
public static void main(String args[]) {
Scanner scn=new Scanner(System.in);
int N = scn.nextInt();
int nr = (2*N)+1;
int nst1=1;
int nsp=(2*N)-1;
int nst2=1;
for (int row=1;row<=nr;row++)
{
for (int cst=1;cst<=nst1;cst++)
{
System.out.print("*");
}
for (int csp=1;csp<=nsp;csp++)
{
System.out.print(" ");
}
for (int cst=1;cst<=nst2;cst++)
{
System.out.print("*");
}
if(row <= (nr/2)+1)
{
nst1=nst1+1;
nsp = nsp-2;
nst2=nst2+1;
}
else {
nst1=nst1-1;
nsp=nsp+2;
nst2=nst2-1;
}
System.out.print("\n");
}
}
}