States, Buttons and Utter Ignorance

I am new to Storyline and looked for an answer to this in some of the tutorials but have not seen it.  I am sure this has been addressed many times so maybe one of you will point me in the right direction.

I have a slide with two buttons.  Each button will display a different layer.  The "next" button on each layer needs to take me back to the original base slide layer with the two buttons.  How do I force the user to view both layers before they can advance to the next slide?  I do not want the viewer to be able to advance to the next slide from one of the layers but from the original base slide layer with the two buttons  after they have viewed all the layers.