Sometimes, I feel that manuals are just there for the technical aspect. Try the flash out in different settings and I find you'll learn more and faster.
Simple stuff, I can still help out.
Flash output control. (there are 2 available, one on camera, on on flash) choose which you can control faster (if you only need 1 set) You can multiply the flash control by using 1 set on the flash as well as 1 set on the camera. i.e. if you set -1/3 on the flash and you set -2/3 on the camera, you'll get a combined setting of -1.0
Focal length of the flash is for auto matching with the current lens focal length. The longer the focal length, the small the area you'll be aiming at (as such the flash can focus at a smaller angle range and push more power to the further distance)