How to actually use Iterable and Iterator?

Java Iterable Iterator

Here's codes I got for my assignment for Algorithm week4, but in fact I still don't really know how to implement Iterable and Iterator.

  public Iterable<Board> solution(){                     
    Iterable<Board> iterable;
    if (isSolvable()) {
      iterable = new Iterable<Board>() {
        @Override
        public Iterator<Board> iterator() {
            return new SolutionIterator();
        }
       }
    } else {
        iterable = null;
    }
    return iterable;
  }
  private class SolutionIterator implements Iterator<Board>{
    int index = 0;
    @Override
    public boolean hasNext() {
        return 0 < solutionBoards.size();
    }
    @Override
    public Board next() {
        return solutionBoards.get(index++);
    }
  }