To clear a level, fill up the red bar at the top of the game. If the red bar is depleted, it's game over. (Clearing tiles fills up the bar; passing time depletes the bar.)
To clear tiles, create rows or columns of 3 or more of the same color. To do this, swap adjacent tiles by clicking them each once.
Bombs: If you create a row or column of 3 or more gray tiles, a bomb is ignited, clearing all tiles on the board. A new set of tiles will drop down if you still haven't cleared the level.