The scenery.cfg file is a text file that has the different sceneries in your CFS2 installation. The stock installation always has a scenery.cfg file which has a standard set of sceneries. But the user can install additional sceneries by placing the additional scenery file in the ADDON folder or the SCENEDB folder. The additional scenery file can then be added to the game via the settings button and then the scenry library button or by manually typing it into the scenery.cfg with Windows Notepad. it looks like this when opened with Notepad:
[General]
Title=CFS2 World
Description=CFS 2 Scenery data
Cache_Size=64M
Clean_on_Exit=TRUE
[Area.001]
Title=Default Scenery
Local=scenery
Active=TRUE
Layer=2
Required=TRUE
Remote=
[Area.002]
Title=Terrain
Local=Scenedb\world
Active=TRUE
Texture_ID=1
Layer=1
Required=TRUE
Remote=
[Area.003]
Title=CFS1 Library
Local=Scenedb\library
Active=TRUE
Layer=3
Remote=
Required=FALSE
[Area.004]
Title=Airport Facilities Data
Local=Scenedb\AFDFiles
Active=TRUE
Layer=4
Required=TRUE
Remote=
[Area.005]
Title=Scenery Ships
Local=Scenedb\Ships
Active=TRUE
Layer=5
Remote=
Required=FALSE
[Area.006]
Title=Aircraft Weapons
Local=Scenedb\weapons
Active=TRUE
Layer=6
Required=TRUE
Remote=
[Area.007]
Title=Vehicles
Local=Scenedb\veh
Active=TRUE
Layer=7
Required=TRUE
Remote=
[Area.008]
Title=Effects
Local=Scenedb\fx
Active=TRUE
Layer=8
Required=TRUE
Remote=
[Area.009]
Title=Runways
Local=Scenedb\runways
Active=TRUE
Layer=9
Required=TRUE
Remote=
[Area.010]
Title=Buildings
Local=Scenedb\inf
Active=TRUE
Layer=10
Required=TRUE
Remote=
[Area.011]
Title=FS2000_props
Local=Scenedb\fs2kprop
Active=TRUE
Layer=11
Required=TRUE
Remote=
[Area.012]
Title=mr_philippines_no1
Local=ADDON\mr_philippines_no1
Remote=
Active=TRUE
Required=FALSE
Layer=12
[Area.013]
Title=mr_philippines_no2
Local=ADDON\mr_philippines_no2
Remote=
Active=TRUE
Required=FALSE
Layer=13
[Area.014]
Title=mr_micronesia_100707
Local=ADDON\mr_micronesia_100707
Remote=
Active=TRUE
Required=FALSE
Layer=14
[Area.015]
Title=mr_japan_no1
Local=ADDON\mr_japan_no1
Remote=
Active=TRUE
Required=FALSE
Layer=15
[Area.016]
Title=mr_formosa
Local=ADDON\mr_formosa
Remote=
Active=TRUE
Required=FALSE
Layer=16
[Area.017]
Title=Midway Sand Island no objects
Active=TRUE
Layer=17
Local=SCENEDB\Midway 1942
Exclude=N28 12.65,W177 21.03,N28 11.75,W177 19.06
Flatten.0=0,N28 13.60,W177 24.50,N28 13.60,W177 19.00,N28 11.30,W177 19.00,N28 11.30,W177 24.50
Remote=
Required=FALSE
There are several tutorials in the Library on addition of various sceneries. They will teach you about adding any sceneries you want though. A good one is Rami's European install guide - here: