caleb sent me some basic questions about quad copters and after writing this up I decided I should share this with the community...
I can't tell you everything about quad copters, it would take many hours to give you good answers to all those questions. I'll give you a basic overview, but you really need to join that RCGroups site and start reading and asking questions there. It would also be a really good idea to go ahead and buy a quad-copter that is already built, so you can learn to fly with something cheap and durable - FPV copters are expensive, heavy, and not durable, if you crash one, it's gonna cost money to fix. You will not be able to fly an APM copter without some experience first. They usually don't fly right on the first go, and you have to be good enough to not crash it while it's all messed up, so you can figure out what to adjust. I've seen quite a few beginners never get their copters to work because they don't have the skills to keep it in the air long enough to figure out what is out of adjustment - and when you crash, you have to start all over again, after you fix the damage.
Keep in mind that a quad copter is primarily a model aircraft - it's a very different thing from a robot, but some of the technology crosses over. Still, it is an RC aircraft for the most part. Even when using auto-pilot units, like the APM, a quad copter is still primarily a radio control aircraft. So, you need to learn some basics about RC aircraft and get some basic equipment like batteries, chargers, a radio transmitter, and a basic aircraft to start with. I personally suggest JR/Spektrum radio equipment, which works with Blade quad-copters - I strongly suggest picking up a Blade Nano or Blade 180QX to learn to fly with.
Here's my review of the latest quad copter from Blade - the 180QX micro quad. It would be good for flying around the house and outside in the yard, it is really durable and can handle most beginner crashes without breaking. It comes with a camera, so you can start to learn how to aim a camera from an aircraft.
This is my review of the Blade 350 QX - it's a little more like what you will eventually need for FPV, but still a little smaller than what we normally want. It has some auto capabilities, but not all the confusing crap the APM has, so it's a good copter to learn with. It flies perfectly right out of the box, no adjustments or anything usually need to be done. As a beginner, that's what you need, so you can learn to fly without having to learn how to program a controller. It doesn't come with a camera but it comes with a GoPro mount, and it can easily carry other cameras that size.
To answer your specific questions, yes the APM drives the electronic speed controllers (ESCs) which plug directly into it, and the speed controllers run each motor. The APM doesn't know what to do without a pilot though, and for that you mount a standard RC receiver and plug it into the APM - you'll need a radio to send commands to that receiver. This is how you control whether the copter is in auto mode or manual mode, and it has various types of auto modes you can switch with the radio - full auto waypoint navigation, altitude hold manual assist, self-leveling manual flight, GPS position hold manual assist, etc... And obviously, you'll need the radio to fly the thing. Contrary to popular belief, the primary mode of operation on these things is "somebody is actively in control" and full auto flying is actually kind of rare. Many people never even get their auto modes to work right, although I didn't have a lot of trouble with it, once I got the manual modes working right.
To send and receive information for a ground control station, like to set waypoints and to view telemetry during flight, you connect XBee radios to the APM and the computer, and use software like "Mission Planner" to connect. I personally use the Android mission planner on my tablet. In my photo I posted, you should be able to see all that - the wires in the front go down to the speed controllers, the wires in the back are coming from the RC receiver, and you should be able to see the XBee's black antenna sticking up, and the wires from it and the GPS go into sockets on the APM.
There's a beginner tutorial for quad copters here, but it's very basic, in spite of being long. There's a lot of stuff he just isn't talking about - building a quad copter yourself is really hard. Mine are all self-built, but I had many years of RC aircraft experience that you don't have yet - and I built mine with 'known' configurations, just copying what others have done.
Still, you should go to the links I posted in the thread about the APM unit - somebody there did a really nice job of compiling all the links together, for everything you need to know concerning APM copters.
Also, 3D Robotics is the company that invented the APM, so I bought my stuff from them. You can save money getting your boards from somewhere else, but the 3D Robotics products are really nice. The other products require soldering and way more setup, and they seem to be having voltage regulator problems lately too, and users have not been receiving the right cables with their stuff - just avoid all that crap and order from 3D Robotics, you'll pay a bit more but it's worth it. Still, like I said, it's gonna be a while before you are ready to buy from them. Learn to fly first - I can't stress that enough - you are the pilot in command even when using auto-pilot stuff.
You aren't bothering me. I think you're a smart kid and I would love to see you be successful on this. We need more kids like you in America right now.