5/12 of Rails Authentication 1 says to add the 'create' action to the users controller thus:
> def create
> @user = User.new(user_params)
> if @user.save
> session[:user_id] = @user.id
> redirect_to '/'
> redirect_to '/signup'
And this works and I can pass the exercise, however I do not understand and cannot see where '.save' for '@user' is defined. Is this a built in function, if so, what does it do?