At the beginning of each new world you'll find a brief tutorial showing you how to use the new tools. This screen comes from the first level, which teaches you the most basic action of the game: how to cut the rope.
In this level, the red character, Lick, uses his tongue to create bridges and barriers, while the balloons and logs work together to hold up (or weigh down) the ropes holding the candy. Popping balloons, creating bridges, and using logs all in the right sequence to feed Om Nom in one shot is the only way to earn all three stars.
At the top of the screenshot you can see there's a small firefly. This firefly walks you through a level and gives you the solution, complete with how to earn all three stars. Don't use your firefly up on the early levels, however, because you're only allotted a set amount and after that you have to pay to use them.