If the file is zipped, than make sure you unzip it to your desktop, or a folder somewhere on your computer.
Open Realflight, and click Simulation -> Import -> Realflight Archive (RFX G3X) -> It will than be imported into Realflight. Once there just go to whatever it was you imported (model, scene, etc) and select it.
Some files have required models,if you don't have the original than it won't work. Say something like the Ion-X extreme on the swap pages, you have to have Expansion Pack 1, which has the base model for the Ion-X.
Ron's Heliproz South