If you are using a database that does not work with EndNote, or if you have print or other physical sources you want to add to your EndNote library, you can add references manually. In EndNote, look in the main menu for "References," then click to add a "New Reference."

This will bring up a blank record where you can enter the title, author, date, and whatever other citation information you need. By default, the "reference type" is "journal article," but you can click the down arrow to bring up a list of all the options available in EndNote: book, book chapter, newspaper article, web page, dataset, and many more.