ASP.NET and the .NET Framework

ASP.NET is part of the Microsoft .NET Framework. To build ASP.NET pages, you need to take advantage of the features of the .NET Framework. The .NET Framework consists of two parts: The Framework Class Library (FCL) & The Common Language Runtime (CLR).

Understanding the Framework Class Library

The .NET Framework contains thousands of classes that you can use when building an application. The Framework Class Library was designed to make it easier to perform the most common programming tasks.
Some Examples are

File class Enables you to represent a file on your hard drive.

Graphics class Enables you to work with different types of images such as GIF, PNG, BMP, and JPEG images.

These are some examples of classes in the Framework. The .NET Framework contains almost 13,000 classes you can use when building applications.

You can view all the classes contained in the Framework by opening the Microsoft .NET Framework SDK documentation and expanding the Class Library node

For Details Visit Here