[pr_fancycorn]

That's because they were showing off the functionality of GeoGraphics. To do that for general images you would just load an image and place text on top of it, with a function like Overlay or ImageCompose:

    img = Import["c:/blah/blah.jpg"];
    ImageCompose[img, Rasterize["HELLO"]]

That's the same Import you'd use if you wanted to read a webpage through a URL, etc.

You're right that it might not be obvious what to search for, but in this case you would search for "image" or "importing" or "overlaying" and you'd figure it out.

Mathematica uses a 'compositional' model like some other functional languages, as opposed to a 'memory' model like system languages, so that could take some getting used to if your background is system languages.