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
Booster_Chilling_Wind.png

Duckling Rain - this booster causes a rainstorm of small ducklings that damage the blocks
Booster_Duckling_Rain.png

Flower Sprouts - this booster causes a plethora of flowers to sprout from the ground, throwing the blocks up and damaging them
Booster_Flower_Sprouts.png