Newbie help with Mapping Toolbox

I am a newbie to MATLAB, coding in general, and the Mapping toolbox. I am trying to import elevation data for CONUS north america. The documentation I have found all assumes you KNOW how to program, in what order to put the functions, etc. I am a complete greenie to all of this would appreciate a detailed explanation of how to import a terrain elevation file of North America (from the very first figure statement) all the way through showing the elevation data in the map. My goal is to thenm figure out to add this elevation data to produce simulation of RF patterns.

ANY help is greatly appreciated as I have found files on the web but the documentation is sparse to know EXACTLy where to start from scratch on importing, scaling and showing the terrain by lat/long analysis.