Use the mouse to select a level on the menu screen. Click the arrows to change the difficulty. Then, use WASD to move, SPACE to jump and ARROWS to look. Jump from block to block until you get to the green flag (in the game) to complete the level. The Random Level button generates a level using Scratch's random number generator, and I tried to make them always possible, but you will sometimes (very rarely though) get an impossible level.