You must collect all the stars on each level. There are a few different types of blocks that you will encounter. Your standard brick that you can plow right through. Solid blocks that you can't pass through and [?] blocks that will fall once you dig out the brick underneath them. You will need to strategize to find the right path in order to collect all the stars. There are times where the [?] blocks will prevent you from completing the level. Also, don't let the [?] blocks fall on you or you die!