You can save references to Zotero from your browser, by ISBN, or by manually typing the information in.
In the Zotero application, the magic wand icon can be used to add resources by ISBN, DOI, or PMID.
If the item does not have an ISBN or does not exist on the internet, you can add it to the Zotero application manually.
To add a citation manually:
Use the paperclip icon in the menu bar to attach a link or file to a record.