You can use Zotero on the iPad browser by installing a "Bookmarklet," a special link that saves items directly to your Zotero account on the web.
You must have a Zotero account, and your iPad must be online, to use Zotero.
When you're on a page with a citation, select the Save to Zotero bookmark. The iPad browser will save the citation directly to your Zotero library online.
For more information, see the Zotero for Mobile documentation page.
Zotero now allows you to use the iOS Shortcuts app to scan a book's ISBN barcode and save the data to Zotero