Not being rude but you sound like you don't know anything at all, you paid a lump sum for a good camera that you don't even know how to use, that isn't the problem, the problem is you have watched reviews yet still don't know what to do?
When I bought my canon 600d I had no idea how to use it, all I wanted to do was shoot videos, for about a month I didn't know what ISO was, shutter speed, aperture etc etc.
So I watched reviews, learned rules, developed my own then through practice I managed to get the hang of it, I suggest you keep watching YouTube videos on how to use DSLRS for filming.
The best way to learn is practice.
I'm surprised you thought of the bmcc considering your out if your depth with a GH3, that camera is another ball game