The code across the top of the screen is highly specific to Microsoft. You wouldn't see this, for example, in HTML pages generated by hand or otherwise, unless you were working with a Microsoft product.
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
The following code shows an HTML document. Essentially, HTML gives structure to web pages. Visual Studio is a very powerful system:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server...