[8FS_Bulau]

I have placed the SAS buttons Mod as shown:
IL-2 Sturmovik 1946\jsgmemods\SAS_Offline_Buttons_v5.8
In that "SAS_Offline_Buttons_v5.8" FOLDER, I have only one FILE: "buttons"
Must I first place the "buttons" file into a "Files" folder which I create inside the "SAS_Offline_Buttons_v5.8 FOLDER"

The basic operation of the JSGME is this:
JSGME will copy whatever is in the folder to the location that you recreate inside the folder. So essentially, what you need to do is duplicate the folder structure in your game install that you want the files to end up.

Example: if you have ...IL-2 Sturmovik 1946\jsgmemods\MyNewMod\Files\part.xxx

When you activate the "MyNewMod" in JSGME, the file "part.xxx" will get copied to IL-2 Sturmovik 1946\Files\part.xxx

Simple?

So, for your SAS buttons, decide where you want that buttons file to end up for you to use it, then recreate that identical folder structure inside your "SAS_Offline_Buttons_v5.8" FOLDER.

In the example that Philip.ed gave, your buttons would end up copied to:
IL-2 Sturmovik 1946\Files\STD\GUI\Game\

If that's where you want it, fine. That is a pretty standard location for buttons. If not, then you need to change the folder structure to be what you want. Keep in mind, that anything that is in the MODS folder (could be buttons) will take precedence over the same file that is in the Files folder. So if you copy a buttons to Files\STD\gui\game, but there is another buttons in MODS\STD\gui\game, then that latter one is the one that will get used.