You control a raven and fly around, you also have an energy and health bar. If you lose all your health you will die (and will be given a chance to restart). You use energy when you dive, and then regain it when not diving (and not trying to either). The raven will move in the direction of your mouse (and can hold your mouse down to boost).
I made this forever ago. It's good enough to share bc I don't use scratch anymore.