Support angle - what does that mean? And other questions...

OK I'm sure that's a newb question. Just got my printer this afternoon, after a couple of minor hiccups* it was printing the carabiner, followed by my first original. Awesome actually, as these things go. 

Though I have a machining background this is my first 3D printer. Have full CNC machine shop for metal. What is the support angle? The angle from vertical at which support will be generated? Or from horizontal? Or the angle of the support structure?

While I'm at it, generally speaking do you just leave the fan on auto and under what circumstances would you not?

Also, it seems a little fiddly to remove the platform for each print - do you all do that, or remove them with the platform in place (which seems like it must be done carefully?

*Hiccups were: button head screws holding magnets for platform were too tight so platform would not drop onto the heads and would not calibrate. Loosened them with supplied wrench, calibrated, and all was good. Next, hardware is version 04 and no choice in software is offered - used version 03. Next, documentation for Mac version of software is not real specific - no left mouse click on a Mac for example. But figured that out.

Welcome to the forum swarf!
If angle is lower than selected angle support will be generated. Simple if statement. :) (see attachment)
Bigger is the part less fan should be used. Part will be stronger if you use less fan but you might lose some details. You use auto fan if you don't have any special requirement of strength or details. If you use too much fan on bigger part layers will start splitting during the printing and warping will occur.
I remove platform while dealing with bigger parts (bigger than a coin).
About hardware version 4:

Thanks, so angle from horizontal. 

I bought the printer with a little apprehension, but so far it has been surprisingly easy to use and makes surprisingly good parts. It seems nicely built and is for the most part nicely thought out. Going to try some larger parts today.