The easiest way to add content to your Mendeley library is to drag and drop PDFs into Mendeley Desktop, where it will then extract the document details, keywords and cited references.
Mendeley will automatically look up Cross-Ref DOIs, arXiv IDs, and PubMed document details.
Manually add files or folders by using the "Add Document" button in Mendeley Desktop or Web. You can also import existing XML, RIS, or BibTex files from databases or other citation managers (such as EndNote).
Mendeley allows for you to manually enter an article's bibliographic entry.
This allows you to add documents other than PDFs, items that aren't in Mendeley's greater research library, items from print citations, etc.
If you already use Zotero to manage your references, you can set up Mendeley to continuously import any documents you add to Zotero. See this page for details on setting up Zotero integration with Mendeley Desktop.
If you currently use Endnote™ or RefWorks for reference management, you can easily import your library into Mendeley:
Mendeley has default filters that appear in the left-hand pane of your library, much like common email tools. These filters are helpful for navigating the contents of your library and locating items within your library:
Mendeley allows you to create folders and subfolders to organize your library by topic, project, or other logical grouping.
Mendeley differs from some email or file systems in that putting an item in a folder does not move the item to that folder. Instead, the folder functions more like a label. This way, you can delete a folder after it is no longer relevant without deleting the contents of that folder; the articles that were in the deleted folder will still be under "All Documents."
For more details, see the Mendeley Guide on Organizing Documents.
Tags are yet another option for organizing the contents of your library. Tags allow for sub-division by topic, subject, or other aspect by using terms of your choice. Tags can be:
Mendeley has a powerful integrated search tool that searches not only your references and document details, but also the content of PDFs and any notes fields.