Use WASD or the cursor keys to move, press SPACE to throw a boomerang, and press X to throw your grappling hook. Hold SPACE to make your boomerang fly further, and press SPACE to call it back. Jump on it to double-jump. Press up or down to go up or down your grappling hook, and left and right to swing.
The grappling hook is one of the most complicated game mechanics I've ever made, and it's still just a little buggy. Have fun messing around! Feel free to use this in your own games!