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.