It doesn't draw at all like we would (though it could), and we would struggle to draw exactly as it does (though we could).
It can draw on things bigger than itself - the question is really "how long is a piece of string?" when it comes to working out it's maximum area.
It's easier to look at what it does, than to explain it, so just have a look.
Step 1: History
physical. For me, it's all too easy to produce digital things which are interesting - programming or mash-ups or virtual experiments are devalued because they are intangible, you can run a hundred, a thousand, a million variations in a day - it's the proverbial roomful of monkeys with typewriters. The output becomes disposable, it get's hard to see the value, the craft.
So 3D printers and other desktop manufacturing tools and technologies (laser cutters etc) have got more and more popular, it's hard to overestimate how much hunger there is for a tangible, physical, touchable, smellable product of all this clever-clever digital work.
So this isn't wholly original, check out this prior art for more inspiration:
Hektor - the daddy of all hanging drawing machines
Der Kritzler - the smartest one yet
AS220 Drawbot - the basis for mine
SADBot - Instructable for an automatic drawing machine on the same pattern by Dustyn Roberts
Or have a look at what I've been doing with mine
Polargraph project code and wiki