1. first go to your clear sky directory for example like mine is: D:\Program Files\Deep Silver\S.T.A.L.K.E.R. - Clear Sky
2. create a new file called: gamedata (note it must be gamedata not separated like: game data).
3. download your mod and extract it (most of the time) using programs like winrar (you can use the trial version).
4. note that most of the time after you extract the mod you will have a file called gamedata, now open the file and copy the subfolders and then paste it into the gamedata file you created earlier.
5. if assuming you have other mods(other subfolders in gamedata), you can avoid overwriting it by just copying the contents into the subfolders.
example: i have a new mod with a config subfolder but i have an older config subfolder already. so i just open the new config subfolder and copy the contents and place it into my old config file with the other mod. you know what i mean, just place both together in one place.
6. if the contents in the subfolder has the same name and requires overwriting, please refer to my other tutorial on editing mods(not yet done).
7. now the important part (skip this if you have done it before), now go back to the clear sky directory and look for a file called fsgame.ltx
and open it using notepad. look for:
$game_data$ = false| true| $fs_root$| gamedata\
and change it into(save it when closing the notepad):
$game_data$ = true| true| $fs_root$| gamedata\
8. congratulations, you have just included a mod into stalker clear sky, thats not so hard was it? fire up your game and see if the mods are included, if not trace back your steps and see what you have done wrong.
9. enjoy your game