Well, I can't write a whole tutorial. But for the basics:
Find a 3D airport you like in RF - choose it mostly for the terrain and the views in the distance (hills, etc.). Photofields are a whole different matter, see the link posted above for those. Skip for now, and consider for later. As you get comfortable, you can figure out how to travel around the 3D world in the editor to find a new location, if you want.
Under Environment, select Create New Airport. It gives you a broad general view, and 4 windows.
Start with "Folder Listing" . Under objects is a "Pilot Spawn" - where you will be standing. Click on it, and note that in the "Properties Windows" details about it are listed.
The third window is the view from the Pilot Spawn location. I usually close it, finding it not that useful.
The fourth window is the Object Palette. Click through the listings, and you can find a ton of items to use. Click on one, and then hit the "Add" button, and it is added to your folder list, and can be seen on screen.
You can then adjust the properties as needed. Usually size and scale are all you really need to play with to start.
Note in the big main window, at the top are view modes and zoom functions. These can help a lot in visualizing what you want to put where. While in these modes, you can grab, drag, and drop objects to place them where you want.
Make sure to download and install the free add-ons - they also provide many, many more objects to use.
From there, it is a matter of playing and creating a few "junk" airports to get a sense of how it works, and exploring the various menus to get a sense of the other options/controls.
For many objects, they may have a huge number of parameters - most of which you never need to touch.
Download other airports, and view them in the editor, to get a sense of how others did things.
