Libraries are collections where you can get to all your documents, music, pictures, and other files in one single place. In some ways, a library works like a folder: you can use it to browse and sort files. But unlike a folder, a library gathers files that are stored in several locations. This is a subtle, but important, difference. Libraries don't actually store your items. They pull from included folders that contain your items, and let you access and arrange the items in different ways. For example, if you have music files in folders on your PC, a shared folder on your network or homegroup, and/or on an external drive, you can include these folders in your Music library so that you can access all of your music files from your Music library.
This will show you how to remove an added folder
from a library
so that it's contents will no longer be included in this library in Windows 8