Feb 16, 2012 07:19 AM|Dino He - MSFT|LINK
A Class Libary will be compiled to a dll file:
And a application will be a .exe or other project file.
You can use reference function to use the dll file.
This is the vedio
it's for a console application, but you can look upon as ASP.net application.
Hope it helpful.
And for more details: