The Google Drive app downloads and installs in a few seconds. Once opened, it asks users to sign in. After you've signed in, you can see your Google Drive documents. "See" is the opportune word here.
Here's how Google describes Google Drive for iOS:
"With the Drive app, you can open PDFs, photos, videos, documents, and anything else stored in your Drive while you're on the go. You can also search all your files, add collaborators to documents, and make files available offline to view them even without an Internet connection."
This is all true. I was able to search my documents with no problems, make them available offline (a.k.a., download them to my iPad), and set up collaborators. That's all easy.
[ Learn more about Google I/O day 1. See Google I/O: Jelly Bean, Nexus Tablet, Project Glass. ]
But you can't edit the documents from the iPad or iPhone in the Google Drive app for iOS at all. Neither online nor offline. You can't create new documents, either. You can't sort through your documents based on date or any other defining characteristic. For example, I prefer to see my Docs listed in descending chronological order (newest to oldest). That's not possible in Google Drive for iOS. The top-most visible document is something I created in 2008. Last, you can't upload anything from the device to your Google Drive account. In other words, Google Drive for iOS is nothing more than a glorified document viewer.
Conversely, using Google Drive in the iPad's Safari browser allows you to do nearly all these things. In the browser, I can create apps in Google Drive, view them, edit them, share them, sort them, star them, download them, and so on. About the only thing you can't do from the browser is upload files to Google Drive.
This leaves me scratching my head wondering why on earth Google bothered to release this application at all. If all you care to do is view your Google documents, then by all means download Google Drive for iOS and enjoy. But if you prefer to actually accomplish things, be productive, and get work done with your Google Drive documents, stick to the browser-based version--or, better yet, your laptop.