I can't tell you much about the library, as I don't use it myself. My method is to make a Library folder (or more) where you keep all your assets (trees, grasses, etc) in handy to find subfolders. Keep that folder there, don't change names or location later, and that would be your main library. Then if you find or buy an object put it there, and load from TG. If an obj, you can save as native tgo after you've changed the internal network to your liking, and save at same location (is what I do).
I think you can set preferences to fill your TG library (which is a different thing from that Library folder) every time you load something, but someone else will tell you.