Randomising images

I am using a child theme of Childishly Simple.
In the Customise menu under Header Image -> Current Header it says “Randomising uploaded headers” Two questions:
1. What does this mean? The site only shows one image?
2. Is it possible to have a header with changing images almost like a photo gallery.

Site is at http://www.s506439810.websitehome.co.uk/warriorswordpress
Many thanks
Tony