For a list of apps on different mobile devices see the Zotero for Mobile support page.
You can use Zotero on the Safari or Chrome 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 browser will save the citation directly to your Zotero library online.