To really understand how and why things work, it's usually a pretty good idea to strip things back to their most basic level and build your way up from there. Maps are no different, if you want to get really serious. The world works in layers, and really good maps that Work will be designed around the same principles. If you want to go the full hog and draw all your layers (and drawing skills aren't necessary, I promise), tracing paper is the medium of choice, because it allows you to stack all your layers on top of each other and see the whole depth of the map at once.
So, if you're going to start at the very beginning (which we all know is a very good place to start O:)), where exactly is that? Not, alack, with a-b-c, or even do-re-me; rather, with transform, convergent and divergent.
Which are what? Plates, of course! Not the dinner kind, but the continental kind.
Modern science posits that the entire crust (outer surface) of the Earth is not one solid shell, but actually a whole bunch of bits of shell (plates) all forming a patchworky kind of crust. And because the centre of the Earth is full of molten rock, and molten rock is hot, and hot stuff tends to want to rise, creating convection currents as it reaches the highest point it can go and then bounces along at the top for a while getting cooler before it sinks again*, these plates move. In fact, if you were to record the Earth from outer space for a significant while and then hit fast forward, the plates fairly zoom around the surface of the world.
So where do transform, convergent and divergent come in? Well, as map builders we care about plates mostly because the edges where they touch each other have the potential to do Interesting Things. To save you the science infodump, here's a pretty picture that explains what they are (click to embiggen):
And here's another pretty picture that shows you where Earth's plates are and what type of boundaries they have (click through for bigger):
One thing should hopefully stand out to you: if you think about where all the major mountain ranges of the world are, they're often along plate boundaries. The Himalayas are where the Indian plate is bashing into the Eurasian plate. The Andes are where the Nazca plate is sliding under the South American Plate. The Alps? Middle Eastern plate smashing up into the Eurasian one. Lots of crashing = lots of mountains.
Of course, plate tectonics at the global level isn't the only reason mountain occur; Australia boasts the Great Diving Range right down its east coast, and you can see in the images that Australia is smack bang in the middle of a plate, not anywhere near a boundary. But in general, plate boundaries are where you have the fun stuff: mountains, volcanos, earthquakes. That sort of fun >:)
How do you employ all this with map building? Very easily. You scribble in some plates, scribble over some continents kind-of roughly based on the plate outlines (but really, you can do anything - look at Australia!), and then have fun deciding where to cause all the chaos >:) Impassable mountain ranges, volcanos, undersea geysers, rifts and trenches both terrestrially and undersea... Bwa ha. So much potential conflict for your poor little characters.Lesson #1 in Map Building: The mountains are where things crash together. So are the volancos and the earthquakes.
Until next time, have fun causing chaos. Chaos #ftw! :D