WPF exists as a subset of .NET Framework types that are for the most part located in the System.Windows namespace. If you have previously built applications with .NET Framework using managed technologies like ASP.NET and Windows Forms, the fundamental WPF programming experience should be familiar.

XAML:

XAML is a markup language ued to construct layout in Windows Presentation Foundation. Asp.net developers will find more easier designing UI on WPF using XAML since its syntax structure is similar to asp.net, aspx pages.

Following example shows you how to create button using XAML.

The following figure shows the user interface (UI) of WPF window with Button that is defined by the XAML in the previous example.

The main behavior of an application is to implement the functionality that responds to user interactions, including handling events (for example, clicking a menu, tool bar, or button) and calling business logic and data access logic in response. In WPF, this behavior is generally implemented in code that is associated with markup like in aspx pages. This type of code is known as code-behind. One of the great featrue of WPF is that it allows the seperation of programming logic and UI with UI and code behind model like in aspx applications.  The following code shows the code behind that also implements buttons click event.