Fb Touch offers a shortcut to the Facebook web application on your Symbian device, so you can quickly see what's happening on the social network.
Since it's a web app link, Fb Touch links in to the web browser on your phone. Click on the Fb Touch shortcut and you'll be instantly transported to the mobile version of Facebook, where you can post updates, view your news feed, send messages to your friends, etc.
The advantage of using Fb Touch to access Facebook is that it always takes you to the most up-to-date mobile version of the service, which is constantly being refined to make it easier to access options and take advantage of Facebook's features.
It's no more than a gateway to the mobile version of Facebook, but Fb Touch is worth installing if you want even faster access to the site.