To add an item not held by the Library, select Include records without full-text access and try searching again.
If you cannot find a record, choose ADD ITEMS +, write your citation details in the form, then select Add.
Tag the citation as appropriate: e.g. Required, Recommended, Library to copy (scan) chapter, Library to source article, etc..
Choose the citation's ellipsis ... and select Send to Library.
(Another option to add citations to your list is using Cite It! See tutorial video: Adding resources with Cite It!)