To use the Candipults simply press Y when you are standing near them. Rotate them using the Analog stick and press Y again to load it. Aim all the candy balls into the giant bowl to complete the level.
Summon over two Oompa-Loompas then head over to the stairs. You will find some machines near by, order the Oompa-Loompas to start working. Augustus should then blow up into the tube.