What we are going to cover in this tutorial is a way (non-destructively) to install Mods/Plugins to your games/apps. The app that does this is called JoneSoft_Generic Mod Enabler (JSGME).
It's portable so it won't need installing on your computer. I use it to install mods to games like rFactor or Automobilista. I also use it to install plugins to OBS Portable.
Download the app and store somewhere on your computer where you keep your portable apps. For this example I will be using Automobilista.
Create a windows shortcut to JSGME. Now the next part is very important otherwise it won't pickup where you mods are.
Go to the properties of the shortcut you just made and make sure the "start in" path is the path to app you are installing mods into, in this case it's Automobilista.
When you first run JSGME it will popup a dialog box asking where your mods will be stored. I usually put "_MODS" (without the quotes) in this box. Make sure you have a folder inside game folder matching whatever you decide to put in.
Extract your mods to the folder you created above. They need to match the structure that they would as if you drag and dropped them in. For an example I downloaded a mod called "AMS-Historic-Estoril" and extracted it to a folder in _MODS named the same. Inside this folder is the "gamedata" folder of the track mod.
If you have followed the steps correctly above and open JSGME you can see the mod in the left panel. To enable this mod, highlight it and press the > arrow in the middle and it will move to the right panel under "Activated Mods". Depending how big the mod is, it might take little bit of time. The app may not respond for a while but it comes back to life once the mod is copied across.
To remove a mod just highlight in the right panel and press the < arrow.