If a blue ball has a 4 with an arrow pointing down, then you should place that ball on a black dot. It will cover that dot and the next 3 black dots going down.
Not sure how many levels there are.  Or how points are scored for the Leaderboard.  At the moment, I'm #2 out of just 9 players.  I've solved about 25 levels.

https://apps.apple.com/ca/app/drop-filler-puzzle/id6444165171?uo=2