Currently there is no official Facebook app in the Windows Store although some features for reading, accessing and sharing on Facebook are baked into the Windows 8 OS if you have shared your Facebook credentials with your Microsoft Account (formerly known as Windows Live ID).
Information from Facebook appears in your People Hub/Tile and from within there you can send and reply to some messages and others require use of the Messaging Hub/Tile and that is mainly for Facebook Chat.
In both of those situations there is no way to share a picture from within the Windows 8 OS to your Facebook friends like there is in Windows Phone.
So I am happy to let you know that the ability to easily share pictures with your Facebook family and friends is coming to Windows 8 via the Facebook Uploader App from the Auri Group.
The app, Fu for short, will integrate into the Windows 8 Charms Bar under the Sharing option and will let you share a picture either directly to your Facebook Timeline or add it to an existing Facebook Album.
Here is a graphic from Auri Rahimzadeh the developer that shows the sequence to use it:
According to Auri the app is in the final stage of approval for the Windows Store and he expects it to be available in the Windows Store within the next week. Once it arrives he told me that he looks forward to your feedback so he can further enhance the app to make it a useful part of your Windows 8 experience.