what is the procedure for that like simple add code in App_code folder
No special step needed. Just place the class file in the
App_Code
folder.
When you add just a class to the root for the first time, it should ask you to place it in
App_Code
folder. If it does not exists, it creates one. In case this has not happened with you then, try creating the folder manually and place the class file there. (Once you create the folder, it's color would automatically change to some other color then a general folder color.)
It's just that, if we store any class files (like .cs or .vb), ASP.NET handles files in special ways - compiler compiles them automatically. Putting class file now by creating
App_Code
will not do anything as its a compile time thing! This article would be a good read for you:
Shared Code Folders in ASP.NET Web Site Projects [
^]
Also, have a look at this article:
Beginner's Guide to ASP.NET Application Folder[
^]