The way to get mods working is to place the folder containing the modded files in the Soldat\Mods directory. The folder should have other folders in it, like Weapons-gfx, Sfx, Interface-gfx, etc. So, the sound effects for the Nerf Mod 2 would be in Soldat\Mods\Nerf Mod 2\Sfx.
Once that's done, you can use Soldat's built-in Mod Starter (a rip-off of mar77a's Mod Manager) to choose the folder and hit "Run Soldat Modded". That's it, Soldat should run with the graphics and sounds from the selected mod folder.
Or, you can be a hardcore person like me and
make a shortcut for easy access to your mods.