We assembled our quadcopter from a kit, which included an electronics package that basically just needed to be mounted and plugged in. Our primary reference was this website, which is easy to follow and full of comments that address many of the problems you'll encounter (really, these forums and others you'll find on the web are invaluable):
It's no longer being maintained, though. The new site, while cleaner and easier to navigate, doesn't seem to have the wealth of information yet.
For now, I would recommend using both in tandem.
UPDATE: as we posted earlier, 3D robotics has released this assembly manual. It would have saved us literally days of deciphering inferior instructions. Check it out.
APM - Ardupilot Mega. Ours is version 2.5. The latest is 2.6. This is the system we're using, but others on the market include the Naza and DJI's system. This is the hardware that runs the drone, its brains.
RC - Remote Control. duh?
Deans plugs or connectors - this a type of electrical connection. A lot of people have strong opinions about these as opposed to XT60 connectors. A quick google search will bring you to pages and pages of debates about the relative merits of each. We've got both on our quad.
ESCs - Electric Speed Controls. This is the circuit that transmits power from the power distribution board to the motors. It allows you to vary the speed of the motors. Typically, it will have a low-voltage cutoff point, so that if the voltage drops below a certain level it will cut power to the motors, protecting the battery.
PDB - Power Distribution Board. The PDB splits power from the battery and sends it to each motor via an ESC.
Power module - NOT the PDB. The power module connects the battery to both the PDB and to the APM. It powers the motors via the PDB and it powers the APM, which it is attached to with a 6-pos connector. The power module also monitors current and voltage.
Servos - A servo is a small motor that controls a mechanism or system. In this context, it often refers to the servos that control gimbal rotation (camera angle).
Gimbals - A gimbal is a support system that can pivot around one or more axes. In the context of a drone, it most what holds the on-board camera.
UAV - Unmanned Aerial Vehicle
XT60 plugs or connectors - a type of electrical connection (see Deans above).
