when you install/download a mod, what do you do next? i can't get it to work!

It depends on where your Soldat folder is located. It is very probable that your folder is located in Program Files, so when you extract it, click on the shiny button that says "Browse." Click on the little plus beside My Computer, then C:, then Program Files, and then Soldat. If you cannot find the folder then do a search on 'Files and Folders' with the name Soldat. This is where you extract mods. While extracting, a prompt should ask you if you want to replace any files. To make your life easier, click on "Yes to All." If I were you, I would create backup files before installing a mod.

you don't need to do copy and paste (only with some mods). With most of the Mods you can just dezip the archive into the main folder.