I've just noticed that Orbx have issued a new version of "FTX – The Definitive Guide", this one dated May 2016. (If you've got an older version you'll find that it isn't vastly different, but it has been updated in places).
The Guide tells you about all the stuff you need to know when installing (or uninstalling) Orbx scenery — how to use the insertion point to get the Orbx files at the correct position in your scenery.cfg hierarchy, the place and function of the various Orbx scenery offerings in what they call 'the simulator "Layer Cake"', useful options when using FTX Central, th