There are two different ways of installing mods (assuming that you have downloaded a .zip file with the mod in it)
First of all,
if you don't already have a program such as winrar.. Get it.
It lets you easily access the content of .zip files. - just google for winrar
With winrar installed you should be able to
right click on the .zip file with the mod in it
and pick the option 'explore' which will open the zip file in a new window and show its contents.
Now you have to
chose if you want to overwrite Soldats original files with the mods files.. or install the mod using the infamous "mod parameter" which will not affect original soldat files (except if you want to replace the HUD interface files which for some reason don't work with mod parameter)
If you just want to overwrite the original Soldat files:- open the .zip
- find the folder inside which has everything in it (it's probably named Soldat or the name of the mod)
- copy the contents of that folder to your soldat directory.
If you want to install using the mod parameter:- (using the same method as above) copy the mod folder to your soldat\mods directory (if you don't have a mods folder in your soldat directory simply make one)
- if the mod folder is named soldat you should rename it to the name of the mod
- then make a shorcut to your soldat .exe and add
-mod "modfolder" on the end of the target line (replacing modfolder with the name of the folder)
Now when you run the shortcut it should start up soldat with the mod running.
- If the HUD interface (ammo bar, health etc) that came with the mod doesn't work with the mod parameter you can overwrite the original soldat files in Soldat\Interface-gfx
For more help with using the mod parameter visit:
http://wiki.soldat.nl/Mod_parameter