You can always manually add citations to Zotero, if you are not able to add information in any other format. When you use the New Item tool, Zotero will create a new blank citation that you can fill with information for your citation. You must choose an item type, to create a new citation, but the item type can always be changed in the citation information panel on the right.
Click the image to the right for a larger version in a new window.
Click the Add Item icon (green circle with a white plus icon).
Choose the item type you'd like to add (ex: Book Section or Journal Article).
In the right sidebar, click into the boxes for each type of information you want to add (ex: Author, Publication) and type or paste the citation information.
To change the itme type, click Item Type in the right sidebar to update the citation type.