There are currently no official apps available for Zotero, but an iOS-app is under development, and there are some tools and a few third-party applications that are available and useful.
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.