java sort using anonymous class

I have class in which I am sorting a list.

import java.util.*;

public class First 
{

    private static HashMap<String,Second> msgs;

    public static void main(String[] args) 
    {           

    List<String> ls=new ArrayList<String>();


   ls.add("fourth");
   ls.add("2");
   ls.add("second");
   ls.add("first");
   ls.add("third");
   ls.add("1");

   Iterator it=ls.iterator();

   // before sorting
   while(it.hasNext())
   {
     String s=(String)it.next();
     System.out.println(s);
   }

   Collections.sort(ls, new Comparator(){
       public int compare(Object o1, Object o2) {
           return -1;
           // it can also return 0, and 1
        }
    });

System.out.println(" ");

//after sorting
   Iterator iti=ls.iterator();
   while(iti.hasNext())
   {
     String s=(String)iti.next();

     System.out.println(s);
   }

}


}

After the program is run, I get these values:

1    
third
first
second
2
fourth

My question is what is the behavior of Collection.sort() function here. On returning -1 from compare function, we get the reverse order of the list. Then how can we get other sorting orders? What is the role of returning 0, and 1?

Finally, I modified the sort function in this manner to get sorted data.

 Collections.sort(ls, new Comparator(){
      
      public int compare(Object o1, Object o2) 
      {
          String sa = (String)o1;
          String sb = (String)o2;
                            
          int v = sa.compareTo(sb);                             
          return v;  // it can also return 0, and 1
         
       }
 });