You can use shapes to create masks of photos. Click Shape and add a shape to the presentation. Then click Media > Photo and drag an image into the Shape. The shape will create a mask for the image.

Choosing File > New in Keynote opens a theme chooser; a collection of templates that have distinctive design styles. Although you might want to start with a blank canvas there is no option to do so.

Since 2014’s “Prototyping: Fake It Till You Make It” WWDC session, Apple’s Keynote app has become a popular tool for designers and developers looking to make quick and easy app prototypes and concepts ...