Okay, I know just enough about this to be dangerous .
I have imported several planes but I'm having trouble with the add-on.
I downloaded add-on RFAOV3_G4 and extracted the files. But I don't see them in my plane or airport files?
They were referring to the free Addons from Realflight. You can download them from https://www.realflight.com/rfl-kb-rf9.html
Scroll down the page to find the Addons, they are listed under the "Compatibility" section. Also look at the 'How To" section lower down the page for instructions on installation.
Most of the Addons aircraft are included with RF Evolution.