Here are the description for the each folder in asp.net 2.0 that we have to create for diffrent purpose.
App_code folder contains the code files for the classes, structures,enums etc. It also contains .wsdl files for web services. Typed data set files are also reside in this folder.Any of this item automatically available to whole application.
ASP.NET supports themes to enable visual styles on web page. This folder contains the themes skin and .css(Cascading Style Sheet) files.
App_Data contains the database for a application and other data files like .mdf,xml,text and .csv files used in web application.This folder are used to stored data related entities.
ASP.NET allows us to create resource files. There are two types of resources files one is global and another one is local. The global resources files are available to whole application. While local resouces files are available to specific page only. This folder store global resource files with .resx extensions.
This folder stored local resources files.
This folder store web reference of web service from a asp.net 2.0 application. You can web reference via right click project in solutions explorer and then click add web reference.
The App_Browsers folder holds browser files, which are XML files used to describe characteristics and capabilities of these browsers
This folder contains assembly files for controls and web pages.Assembly files are basically a .dll files. Any .dll files found this folder automatically links to whole application.
This folder structure are basically supported by asp.net 2.0. You can also create your own folder structure by right click project name in solution explorer. and add new folder.