Adding graphic background to the stage

Hi

I'm a Creative Cloud user so I have the latest version of Edge Animate.CC 2015.

I'm creating a slideshow using a template I purchased on the web, that uses symbols for each slide. 

I am digging through the tutorials but am not clear on how to add a background image to the stage  I see how to easily add a background color, but am not sure how to add a graphic, taking advantage of Edge's latest version.  I want that background to show for the entire slideshow. 

Do I still need to to type in some code?  And if so, where do I do that.  I guess I can't just browse to the image.

Your suggestions are appreciated!

Thanks

Rowby