Zotero has an app for iOS and you can download it from App Store.
You can work with and edit your references on your mobile/tablet by using Zotero Web Library. Go to Zotero.org and choose Log In from the menu to access your Web Library.
You can also install the Zotero Bookmarklet in your browser. This will make it possible to import references directly to your Zotero Library.
An overview of all available mobile apps can be found on Zotero.org.