How to Manage Permissions for a List, Library, Folder or Document Item in SharePoint
Login to the SharePoint 2013 site as an administrator.
Navigate to the list, library, folder or document item for which you want to assign a unique permissions.
In the Library tab click on Shared With button in the Settings section (If you want to manage permissions for a folder or documents, select this folder or item and click on Shared With button in the Files tab).
In the Shared With window click on Advanced.
Click on Stop Inheriting Permissions in the Inheritance section to create unique permissions for a library (list, folder or document item).
Click OK in the dialog box appeared.
Click on Grant Permissions.
Enter the email address as username of a user for whom you want to grant permissions in the Invite people box and click on Show Options.
Select a permissions level for this user from the drop-down menu.
Click on Share.
Now you can see that this user has been granted unique permissions for this library (list, folder or document item).
