In iOS 6, linking your Fb account couldn’t be simpler. Tap on the Settings app, scroll down to Fb, Tap it, install it if you haven’t already performed so, then enter your username and password.
Lastly, Tap Sign In and your Fb contacts might be added to your iPhone. Calendar info will even be added.
Word that there’s a Settings button just above where you put in your username and password. This is where you'll be able to enable or disable alerts for chats and messages. For different notifications, you’ll need to use the settings inside the Facebook app itself.