There are two ways to add a document to your Mendeley Desktop library:
One quick way to add a document to your Mendeley library is to drag and drop the document into the open Mendeley window. For the document that is not recognized by Mendeley, you can manually type the missing information or search the title on Google Scholar.
One of the best ways to organize information on your library is to create folders and sub-folders. You can create folders for your projects, classes, and more. Also, you can organize your library by adding tags to your documents.