Every aspect of SharePoint is highly customizable from the page layouts to the individual controls on the page. Customization of controls allows better functionality according to the needs of the users and enhances the user experience when using the site.
Functionality on SharePoint can be customized using the .NET framework. For example, the left navigation bar will only present links that a user is authorized to use, this is controlled by the security settings within SharePoint, but this requires management of these rules for each individual that could get involved. Instead, customization of the navigation bar using the .NET framework can allow implementation of complex logic which will provide access to links based on the results of this logic.
SharePoint Web Parts
Web parts are server controls which can be added to Web Part zones on a SharePoint page. These controls allow users to modify the appearance, content, and functionality of a web page. SharePoint provides a variety of built in web parts such as announcements, contacts, calendar, task lists, etc that can be added by the user with a few clicks of the mouse. In addition to the built in web parts, SharePoint leverages the reliability, scalability, and functionality of ASP.NET version 2.0. This includes support for the ASP.NET version 2.0 Web Part Model (with added backward compatibility support for Windows SharePoint Services V2 SP2 Web Parts). Building on ASP.NET not only provides a deep technical foundation for WSS, but also allows WSS to leverage the Visual Studio development environment for application development.
SharePoint Template Creation
When you install Windows SharePoint Services, a single default master page is applied to all the pages in a site. You can, however, create your own master page templates for a site and make them available to the site and sub sites. Such customization allows you to incorporate company branding into the SharePoint site and provide users a familiar interface.