In order to clear a level, you'll need to reach all the goals required in the moves allotted.
You can see the goals for a level when you first tap on it: a screen will pop up with your goals listed in the top right. The goals for a level will also show while you play in a bar above the board.
Goals can include:
- Clearing off a certain number of a certain piece
- Clearing off obstacles
- Reaching a certain score