If you've ever seen the main FSX folder, you'll have seen these names before. So inside the file you downloaded, you might see folders called 'Modules', 'Effects', 'SimObjects', 'Sound', 'Gauges', etc. If yours looks like #3, follow the instructions after that. If yours looks like Picture 1 or 2, follow the instructions immediately following. Or it's just a folder that contains these kind of files: It should look something like the following:
#Steam flight simulator scenery downloads zip#
Your download will be a zip file, so extract it somewhere and then open it up.
It is important to follow any special instructions the authorr says you should follow that may not be specified in this guide. So by now, you've chosen an airplane you like, downloaded it, but you don't know what to do with this mess of files. Not nearly as complex as PMDG, for example, but not default aircraft simple.