How do I retrieve user information from cookie?

Hi,
I'm using Facebook authentication in my new MVC 5 app. I see that in Startup.Auth.cs, there's a line that tells the app to store the authenticated user information in a cookie.
I want to better understand what's going behind the scenes there.
Once the user is authenticated and logged in, how do I retrieve user information stored in a cookie? Are the data stored in the cookie encrypted? Can I store additional information there?