If you wanted a mod, you should read this.
[Mods that gives you extra parts]
[WARNING: RSS AND PLANET MODS NOT INCLUDED]
1. download any Parts Mod.(Simple)
2. Go to KSP Folder and if a GameData file appeared in the download, go take whats inside it and place it into /Kerbal Space Program/GameData.(Confusing)
3. Thats it, but if you see a ModuleManager File Put it Into /Kerbal Space Program/GameData same as step 2.(Simple Again!)
Important: Any Mods that gives a new Celestial body or any structure or RSS Will not work on these steps. Sorry.
Hope this works for you, and comment if this works or not.
Also Subscribe to my Youtube Channel if you want to do it.
GOOD LUCK EVERYONE ON YOUR FIRST MISSION WITH MODS!