Creating additional document libraries is a method of separating data. Document libraries can have unique permissions when combined with User Groups.
The use of document libraires in the pursuit of hiding data is helped greatly by the use of User Groups. Please review this guide to create and manage User Groups: Creating and Managing User Groups in SharePoint
I have my User Groups created; how do I use them with Document Libraires?
Create an additional Document Library
Navigate to s.uconn.edu/sharepoint.
Click on your SharePoint site to view it.
Click on Home to ensure you are on your Home page of the site.
Click on + New and choose Document Library.
Give the new Library a name.
Click on Create. The Library can now be filled with files and folders.
Create unique permissions for this Document Library
In these steps you will isolate this library from the permissions of the other(s) and create new permissions for it.
Click on the Library in the left hand menu to view it.
Click on the settings gear in the top-right corner of the screen. Click Library settings in the popup menu.
If you need to change the libraries name in the future, you can do it from this menu. Click on More library settings.
Click on Permissions for this document library.
Click on Stop Inheriting Permissions to isolate this library from the permissions of the other libraries.
Check the boxes of the User Groups that you do not want to view this library.
Click on Remove User Permissions.
The remaining User Groups will be able to view this library.
Click on Grant Permissions to add a new user or group.