So Ive started a mod in which I plan to use armor someone else created ( With permission ), but after loading the skyrim.esm and the armor plugin I want to use when I add it to the inventory of an NPC nothing shows up. I'm pretty brand new to modding so there is probably something simple I've done wrong. This also happens when I tried to give an NPC the ancient nordic armor but as far as I know those are the only instances that the problem occurs. Any help would be great.

Someone needs to write an explanation of mod isolation in the CK wiki...

I'm not good at explaining things, but basically, a mod file can only use resources from itself or from one of its master files. Using the CK, there is no way to set one esp file as the master of another esp file.

If the armor plugin that you're using is an esp file, when you save your mod, the armor plugin is not saved as a master of your file. If you open up your file in the CK again, you will be bombarded with errors because your mod references objects from something that doesn't exist (since the armor plugin is not a master of your mod).