Web forms are pages that users request through the browser. These forms the user interface that gives look and feel to the web applications. Web forms are contained in files with a ‘.aspx’ extension. These pages are built using HTML, ASP server controls, user controls and server code. Whenever a user requests a page. It is compiled and executed on the server based on the compilation model, the HTMLmarkup is generated which the browser can render.

In Visual Studio, under Solution Explorer, one can see the .aspx file and under .aspx there is one .aspx.cs file and one .aspx.designer.cs file.