Use the WASD keys to move. Space to throw the boomerang towards the mouse pointer. Try to hit as many apples as you can before time runs out!
This is featured on the "Invent with Scratch" screencast by Al Sweigart at http://inventwithscratch.com/boomerang-game/
Learn to program games with this free online Scratch course: https://inventwithscratch.com/class