If you get a fake email that looks like it is from Facebook, you can report it to Facebook simply by forwarding it to a new email address that was just set up by Facebook. Forward your suspicious email to email@example.com. That is all there is to it.
We have warned people that they should never click on a link in an email without first confirming where the link goes, or that the email is genuinely from the sender, or that you are expecting the email, as when you sign up for an online account and they send you a confirming email.
Here is a picture of a fake Facebook login page created by some clever phishermen. Even though it looks genuine at first glance, there are differences. Looking closely at the address line is you best bet, but this image illustrates the other differences as well. Tip of the cap to Sophos again for the graphic.