Click on Behavior in the left dashboard. Frequency is if you want the user to always wee the bar or only every 24 hours or whatever time you set up. It is small so I am going to leave it all the time.

Placement is a selection for having the bar move along with your reader or being in a fixed position. I will do move along with reader. And then just have your Facebook URl in the next box. Click the green save button when done.