A couple of places to find the FB icon on S6:
-On the sign-in page http://www.society6.com/login
-On the header next to sign in
-On the right side of the post page http://www.society6.com/post
-On your settings page http://www.society6.com/settings/facebook
If you haven't used this on other sites you'll find that it's pretty easy. Just click the icon to link your account, log into Facebook (if you're not already logged in) and then authorize the accounts to be linked. Once you complete this process all your Society6 posts will become updates on your Facebook feed. If you haven't yet, also add your Twitter account too so your Posts get updated in both places.
We'll be adding more features using Facebook Connect and Twitter authorization down the road so stay tuned. We know how important it is to reach the audience you've worked so hard to assemble, so we want to make it easy for you to do that all from Society6.