Press space or click for the next slide. Better in full screen. It's short and simple. Just follow the red oval.
If you download your Scratch project, whatever happens to it, it will be safe, this shows you how to download and upload your projects. While you can just click "save as a copy" in the "File" menu, if your Scratch account gets hacked or deleted, this method would help you recover your project on a new account. Just ignore the screenshot in the bottom right corner.
