The best way to add sources to Mendeley is by using their web importer. This is a web browser plug-in that can recognize information about a journal article, ebook, or website when you are viewing the source in a database or web page. (Information about installing the web importer was available through the link on the "Getting Started with Mendeley page of this guide.)
When you are on a web page with the full text of a source:
You can also add sources to Mendeley manually. You will often need to do this for print sources or for uncommon online sources such as PDFs of reports. (You can also use this method if the web importer doesn't work.)
Follow these steps:
You can transfer a library of sources into Mendeley from other citation managers like RefWorks or Zotero. This process will only send over the information needed to cite a source such as authors, title, and publication date. If you have been storing PDFs in the other tool you will need to move them separately.
Although the process will vary slightly between different tool, this is the general process for moving sources into Mendeley.
If you have difficulty finding the export option in your current citation manager, look up their help guides online.