How do I make a wallpaper on my navscreen or create a screen saver? Id assume a pic of a usb flash drive ? Thanks for the help in advance.

 

You need to import the pictures from usb drive to MDX's HDD. Go to setup & wallpaper.
Manual says you can import 10 but mine only did 6, may be due to size, I dont know.

The wallpaper will show only one that too when you do not press Ok for the Nav warning.

Detailed steps are available in Manual, ask here if its still confusing.