These components include Visual Studio Express 2012 for Web, IIS Express, and the .NET Framework. You can use these tools to create ASP.NET web applications. You can also use the Microsoft Web Platform Installer to install free ASP.NET and PHP web applications.
https://msdn.microsoft.com/en-us/library/dd537667(v=vs.110).aspx
Visual Studio Express 2012 for Web supports ASP.NET Dynamic Data. Dynamic Data lets you create extensible data-driven web applications by inferring at run time the appearance and behavior of data entities from the database schema and deriving UI behavior from it.
https://msdn.microsoft.com/en-us/library/dd537667(v=vs.110).aspx
By default, Visual Studio 2012 and Visual Studio 2013 use IIS Express. For more information about about how to specify one of the alternative web servers, see How to: Specify the Web Server for Web Projects in Visual Studio.
https://msdn.microsoft.com/en-us/library/58wxa9w5(v=vs.120).aspx
Security Context for IIS Express. An important difference between the development servers in Visual Studio and IIS is the security context in which the servers run your ASP.NET pages. This difference can be a source of problems when you deploy a web site or web application to run on IIS.
https://msdn.microsoft.com/en-us/library/58wxa9w5(v=vs.120).aspx
You can use Visual Studio Express 2012 for Web to create and work with ASP.NET websites and Web Application Projects in the following configurations: File system websites In a file-system website or Web Application Project, files can be in any folder.
https://msdn.microsoft.com/en-us/library/dd537667(v=vs.110).aspx
Webpages and Web Server Controls. Visual Studio Express 2012 for Web helps you create both ASP.NET webpages and HTML pages. ASP.NET webpages are dynamic pages. They include ASP.NET web server controls and code that ASP.NET processes on the server.
https://msdn.microsoft.com/en-us/library/dd537667(v=vs.110).aspx
In earlier versions of ASP.NET, when you use Visual Studio to create a new Web Site project or Web Application project, the resulting projects contain only a Default.aspx page, a default Web.config file, and the App_Data folder.
https://msdn.microsoft.com/en-us/library/s57a598e.aspx
Web Servers in Visual Studio for ASP.NET Web Projects. When you develop web projects in Visual Studio, you need a web server to test or run them. Visual Studio lets you test with different web servers, including IIS Express, Internet Information Services (IIS), External Hosts, or Custom Web Servers. You can use any of these web servers with a file-based web application project. For a file-based web site project, you can use IIS Express.
https://msdn.microsoft.com/en-us/library/58wxa9w5(v=vs.120).aspx
What's New in ASP.NET 4 and Visual Web Developer. The .NET Framework 4.5 includes enhancements for ASP.NET 4 in targeted areas. Visual Studio 2010 and Visual Web Developer 2010 Express also include enhancements and new features for improved Web development. This document provides an overview of many of the new features that are included in the upcoming release.
https://msdn.microsoft.com/en-us/library/s57a598e.aspx
In addition, you can create folders for special purposes, such as for storing source code, defining themes, and managing resources. Visual Studio Express 2012 for Web includes an ASP.NET Empty Web Site project template and an ASP.NET Web Site project template.
https://msdn.microsoft.com/en-us/library/dd537667(v=vs.110).aspx
which visual express for asp.net
Visual Studio Express 2012 is used for ASP.NET.  Visual Studio Express 2012 is for ASP.Net.