class or not class?

I have the following code in an exercise and in the video shown the Page is a class but when I try to re-create the exercise it does not "turn" into a class.
In the video nothing special is done or said about it and I have checked my exercise to verify that it is exactly the same but I don't know what the difference is or what I am supposed to do.
Can somebody please explain to me what is happening here?
if (Page.IsPostBack == false)
{
TextBox1.Text = "";
}


...