First things first, many thanks to the Devs and Modders behind this site. It has changed the way my family and I look at gaming on PC's. Also a shout out to Katherynliza, very informative and patient while not obligated to be either, you rock my socks. <3 Just wanted to offer a thought for those having troubles with the + button while trying to add mods manually. I had the same issue until I noticed the bottom button in the sidebar to toggle mod view, which changed the UI to a more familiar (for me at least) Mod Organizer layout. In this view all mods were listed so long as they were in the folder designated during initial setup of NMM. From here installing is as simple as a double-click. If that doesn't help then it seems to me that your NMM installation may be bugged or corrupt. Personally I would re-install, but that's your decision to make as individuals. :) Hopes this is helpful. I'll check back as much as I can to try and be of further assistance if requested.