Slide Masters Always a Problem

The Slide Master is the master version. Anything you put in the master will appear on every slide that uses that master.

Think of it like a teacher creating handouts with a template from a workbook. The workbook is the master copy. If the teacher photocopies 20 copies for her students, they'll all be the same. If the teacher adds a handwritten note to skip question 5 on the master copy before making those copies, then she changed the master--and the students will all see her handwritten note.

But unlike those physical copies, it's like you had magic to make that handwritten note appear on all the student handouts even after making the copies. Every time you make a change in the master, that change is reflected in all the copies.

Right now, you're making your changes in the original master copy. Instead of making changes there, if you want to create a single slide, select Close Master View. That will let you edit a single slide. When you're ready to add another slide, select New Slide. 

If you want to change which layout (slide master) is used for a particular slide, select Apply Layout.

I know the workbook and photocopies metaphor isn't perfect (since Storyline continues to update rather than being a one-time physical copy), but does it at least sort of make sense now?