(Beam Shot)

(Bomb)

You can receive free beam shots by popping bubbles 7 times in a row.

Moreover, if you want a bomb, you should clear bubbles that are on the upper lines because bombs are charged by collecting bubbles that fall down from upper-lined bubbles. It means the bomb is charged by remaining bubbles.

Therefore, if you do not have any boosters, you can make free boosters while playing the level.

Hope it helps.