ASP.NET Web Parts:

ASP.NET Web Parts is an integrated set of controls for creating Web sites that enable end users to modify the content, appearance, and behavior of Web pages directly from a browser.
Users can save their personlized settings.
Web Parts provide users with a capability to personalize their a Web application dynamically, without developer or administrator intervention.
Web Part Essentials:
The Web Parts control set consists of three main building blocks: personalization, user interface (UI) structural components, and actual Web Parts UI controls.
Developing scenarios for web parts:
Web Parts can be used in one of three ways: creating pages that use Web Parts controls,creating individual Web Parts controls, or creating complete personalizable Web applications, such as a portal.
UsingWebParts