The coins let you use the ship at the end of the game. If you don't collect them all, then you get a game over. It's probably confusing for the people that get them all on the first try, because there's nothing that tells you that fact (other than the game page's description).

Thanks. The type of game I make usually is just platformers or other arcade-y like things. I'm not very good at making puzzles. But this is my second attempt at this kind of game, so maybe I'll make a harder one next time.