java - Big O - for anew beginner -

possible duplicate:
plain english explanation of big o

i asked knowledge of how use big o notation , stumped because had never come across big o before. have read wikipedia page big o , looked @ of questions posted in stackoverflow don't understand.

my question: can provide explanation of big o in simplest form , provide example of how use in following java method:

public int getscore(int[] dice) {     int[][] dups;      dups = possibledups(dice);      // set catscore     (int[] : dups)     {         (int k = 0; k < i.length; k++)         {             if (i[k] > 0)             {                 switch (i[k]) {                 case 1:                     catscore = category.ones;                     break;                 case 2:                     catscore = category.twos;                     break;                 case 3:                     catscore = category.threes;                     break;                 case 4:                     catscore = category.fours;                     break;                 case 5:                     catscore = category.fives;                     break;                 case 6:                     catscore = category.sixes;                     break;                 case 7:                     catscore = category.sevens;                     break;                 case 8:                     catscore = category.eights;                     break;                 default:                     catscore = category.none;                     break;                 }             }         }     }      return sumall(dice); } 

big o worst case scenario algorithm execute. should see how loop depend on inner loop. sample:

public void dosomething(int n){     for(int i=0;i<n;i++)         for(int j=0;j<n;j++) } 

worst case 100 times iterate. change n 20 , worst case 400 iteration.

this o(n^2).