so what is App_Browsers, App_Code, App_Data, App_LocalResources .. and other Folders of VS website!

Under Visual Studio 2005 , websites may contain any number of specifically named subdirectories, each of which has a special meaning to the ASP.NET runtime. The next table documents these “special subdirectories.”

App_Browsers Folder ---------- for browser definition files that are used to identify individual browsers and determine their capabilities.
App_Code Folder ---------- for source code for components or classes that you want to compile as part of your application. ASP.NET compiles the code in this folder when pages are requested. Code in the App_Code folder is automatically accessible by
your application.
App_Data Folder ---------- for storing Access *.mdb files, SQL Express *.mdf files, XML files, or other data stores.
App_GlobalResources Folder ----------for *.resx files that are accessed programmatically from application code.
App_LocalResources Folder ---------- for *.resx files that are bound to a specific page.
App_Themes Folder ---------- that contains a collection of files that define the appearance of ASP.NET web pages and controls.
App_WebReferences Folder ---------- for proxy classes, schemas, and other files associated with using a web service in your application.
Bin Folder ----------  for compiled private assemblies (*.dll files). Assemblies in the Bin folder are automatically referenced by your application.
If you are interested in adding any of these known subfolders to your current web application, you may do so explicitly using the WebSite ➤Add Folder menu option. However, in many cases, the IDE will automatically do so as you “naturally” insert related files into your site (e.g., adding a new C# file will automatically add an App_Code folder to your directory structure if one does not currently exist).