1. Download the plane to a folder on your hard drive where you know where to find it.
2. If it is a .zip file then UnZip it. It will make sub folders
3. If you then see a "readme" file then read it.
If you see a .exe file then select that and it should install the aircraft for you
If Not.....
You may find more .zip files that need to be unziped.
You need to find the folder that contains the aircraft.cfg file
this is the main aircraft folder.
Right click on this folder and select "Copy"
Find this folder and select "Paste"
Your new plane should now be installed but there may still be more.
If there is a "Gauges" folder then copy it to
It should say that the Gauges folder exists, just click on Ok
If there is an "Effects" folder then do the same with that
If you can't find your new plane in Flight sim then open the aircraft.cfg file in notepad
and look for the "manufacturer"
In this example you should look under "Boeing" to find your new aircraft