Click the green flag. Use the arrow keys to move Luz Noceda. Press the 's' key to tilt to the left and the space bar to tilt right. Collect her friends, avoid Belos, the greenish-blueish-blackish monster, and after you get her friends, go to Stringbean (upper right corner). There is a secret thing you can do, but I won't tell you anything more than it will help you win. If you win, the sound at the end is Belos dying. XP
I got all of the sprites from Fan WIki.