You need to be more specific.
Libraries are merely pointers. They are a way of grouping your folders into categories. Microsoft recommends 4 categories: Documents, Music, Pictures, Videos but you should use what suits you best.
Personally I like having a fifth library associated with the Downloads folder. See how to do that
HERE.
There is also a lot of information about moving default libraries or changing/adding folders to existing libraries in this thread
HERE.