In order to use RadProgressBar control in your projects you have to add a reference to the Telerik.Windows.Controls assembly.
You can find more info here.
Getting started with the RadProgressBar control is pretty straightforward. To begin with, you should include the control in your page by either dragging it from the toolbox in Visual Studio, or manually creating the control. Below is an example of how to create the RadProgressBar control in C# and XAML code:
RadProgressBar progressBar = new RadProgressBar();
You may need to change the Minimum and Maximum values of the control by setting the corresponding properties. The default values are 0 and 100.
progressBar.Minimum = 10; progressBar.Maximum = 20;
<telerik:RadProgressBar Minimum="10" Maximum="20" />