From CNET:
At long last, Facebook as a universal app is finally here and if you're an iPhone or iPad user looking to browse the popular social site, the app is better than ever. On the iPad specifically, it might be the best platform for browsing the site available.
The "Download Now" link directs you to the iTunes App Store, where you must continue the download process. You must have iTunes installed in order to open the link, and you must have an active iTunes account to download the application. This download may not be available in some countries.