How ASP.NET form authentication works: recognising cookies from request

Question

I am reading on form authentication in ASP.NET and cannot understand some moment:

James enters a username-password, they are saved in the db. A cookie from username is created, encrypted and attached to a response. As I understand then, when we get a request we need to recognise that cookie received are from James and so we can show his customised page.

What I would like to understand is how system will retrieve username form cookie and then load his info from db?