This segment includes users who have visited your site from Facebook. There are a couple of ways to set this up, for all your traffic from Facebook or just your paid traffic.
All Traffic From Facebook
This segment includes every user who has visited your site directly from Facebook.
To create this segment, include pageviews where the client referrer contains 'facebook'.
Note: If using this segment for analysis of a users' behaviour directly after they are referred from Facebook, add 'time' criteria to only include the user's current session.
Paid Traffic from Facebook
This segment includes every user whose visit to your site is attributable to an advertising campaign you are running in Facebook.
When setting up your campaign in Facebook, you can add parameters to the urls that help you identify a Facebook-referred users on your site. If these parameters are set up for your campaigns then this data will be stored in Permutive, in the url.
To create this segment, match on the url where utm_source=facebook.