On the CheapTickets.sg's homepage, select 'Multi Destinations' right above the search box, and key in your destinations (up to 3 flights of your journey).
Select the number of passengers flying (adult, child, infant) and the cabin class.
Voila! Your search results will give you the details of your flights. Search for your ideal flight by comparing the prices to get the cheapest flight! Last but not least is to book it right away before the deal is gone!