There are 3 types of Powerups that you can activate by touching them with any of your Bubs (balls).
If you touch a different Powerup while your ball already has one effect on, it will combine the effects.
Explosion Powerup: Your ball is charged with explosives and will cause augmented damage to the next block it touches as well as some damage to any adjacent blocks.
Splitter Powerup: Your ball gets split in 3 smaller balls that fly in different directions.
Ghost Powerup: Your ball now has the ability to pass through blocks, damaging them as it passes through.