Power-ups appear on the game field once you match four or more pieces. These are what's available in the game right now:

Firecrackers explode all neighboring tiles. You can get them by matching four pieces of the same color.

Bombs explode everything within a two-tile radius. You can get them by matching five pieces of the same color.

Dynamite explodes everything within a three-tile radius. You can get it by matching six pieces of the same color.

TNT explodes everything within a four-tile radius. You can get it by matching seven or more pieces.

Shovel: you can remove one piece or one obstacle layer from a tile. This booster is only available once you start playing a level.

Rake: you can clear all the tiles in a column and a row without using a move. This booster is only available once you start playing a level.

Gardening Glove: you can swap any two adjacent pieces or power-ups without using a move. This booster is only available once you start playing a level.