Once you have unlocked the boosters you can choose to use them to help you complete the checkpoint. You can get boosters from reward chests, or by purchasing them from the levels, or from the bundles from the Store.
The available boosters are:
Chilling Wind - this booster changes all the building blocks into glass
Duckling Rain - this booster causes a rainstorm of small ducklings that damage the blocks
Flower Sprouts - this booster causes a plethora of flowers to sprout from the ground, throwing the blocks up and damaging them