Extracting data from Arduino MultiWii Flight Controller
Since you're new to Arduino, I'd suggest beginning with a basic interfacing arduino activity. Once you understand reading and writing digital and analog signals it's pretty much plain sailing from there. You may want to invest some time and a bit of cash in a beginners course on Udemy (try PEter Dalmaris' course https://www.udemy.com/arduino-sbs/) it's a good start. From there, talking to the MultiWii should be a piece of cake. Also, check out http://www.multiwii.com/connecting-elements