ASP.NET Web pages, known officially as Web Forms, are the main building block for application development. Web forms are contained in files with an ".aspx" extension, these files typically contain static (X)HTML markup, X for Extensible markup language as well as markup defining server-side Web Controls and User Controls where the developers place all the required static and dynamic content for the Web page. Additionally, dynamic code which runs on the server can be placed in a page within a block
<% -- dynamic code -- %>, which is similar to other Web development technologies such as PHP, JSP, and ASP. With ASP.NET Framework 2.0, Microsoft introduced a new code-behind model which allows static text to remain on the .aspx page, while dynamic code remains in an .aspx.vb or .aspx.cs or .aspx.fs file (depending on the programming language used)
The IIS(Internet information server) need to run ASP.NET page and IIS server can able to host ASP.NET page in real situation.