Scripts are created when you start your video creation process from the Script Editor.
A Script can not exist without a Project; a New Project will be created when you create a script from either the + button or the New Video workflow. Or, you can enter one of your old Projects to create a new Script in it.
Script Preview, you can preview your Script by hovering over it. It is a slideshow with still images that play at 5x the speed of the video duration, so it’s relative to the slide durations.