Sometimes, a reference you want to cite won't be available in an online database. This happens a lot with older or unpublished references (for example, presentations). In these cases, you will need to manually enter your reference.
Navigate to References > Add New or select the New Reference button:
The Add New Reference lightbox will appear. The fields that you need to fill in will depend on the output style and reference type you select:
Fill in as much information as you have. Below the required fields section, you can also add the reference to a folder, attach a related file, add more information in additional fields, or check for any quirks or exceptions in the output style. When you're done, select Save Reference: