I noticed that some of the addons are photo realistic, IE Using Horizon Gen X. Etc.
Do I need a special program before I can use these, and if so where do I obtain such a program.
I only took up flight simulation since retiring, so I am a newbie at it.
All help greatly appreciated
No, just add it like you would any other scenery.
Just don't load new scenery on top of another new scenery that you added.
Scenery add-ons are made to enhance OEM scenery not to enhance another brand.
The only exception would be an upgrade to one that you added, if the directions tell you to.