Nested For Loops And Strings - Take A String As Parameter And Store It In S

Question: 1. Declare and implement a class named Substrings. The class will contain the following data members and methods:

Data members:
string S

Methods:
setS() take a string as a parameter and store it in S
printSub1(), printSub2(), printSub3(), printSub4() print all substrings of S. If S = "abcd",

printSub1() will print "a", "ab", "abc", "abcd", "b", "bc", "bcd", "c", "cd", "d",
printSub2() will print "abcd", "bcd", "cd", "d", "abc", "bc", "c", "ab", "b", "a",
printSub3() will print "a", "b", "c", "d", "ab", "bc", "cd", "abc", "bcd", "abcd", and
printSub4() will print "abcd", "abc", "bcd", "ab", "bc", "cd", "a", "b", "c", "d".

Alright so after doing some googling and watching tutorials I managed to put together the first two but I still don't exactly understand how nested for loops work, however just a single loop I do understand.

Secondly, the 3rd and 4th prints are completely destroying my brain using for loops, which we are supposed to use. Check out my code below, also keep in mind the 3rd is giving errors and the 4th i had to revert back to the same as the first print temporarily because my code because so messed up. How to understand nested for loops better.

[code=Java]

import java.util.Scanner;
class subString {
String S;
void setSubstring(String SS) {
S = SS;

[Code] .....

Compiling: error for myS.printSub3 and myS.printSub4 is the same as 1 because i had to revert it after ruining the code.