Hi Sopan,
This example shows you how to integrate a RadRibbonView control and a RadRichTextBox to create an MS Word type application. You can get a quick look at the code used to create that example by toggling the Example/Code button at the top right of the example window.
After you toggle to "Code" view, look over to the left pane and select
"TelerikEditorExample.xaml" from the list. Now you'll have the code in front of your that created the example you saw when you first loaded the page. If you need more guidance as how to create your own, you can open the example application locally on your machine.
When you downloaded RadControls for Silverlight, you also downloaded this example. If you kept the defaults when you installed ti, the example solution will be in C:\Program Files (x86)\Telerik\RadControls for Silverlight Q1 2012 SP1\Demos
Open the solution, locate the RadRichTextBox project in the solution explorer and expand it. Inside that folder you have the example code to get you started.
Good Luck and let me know if you need any additional help,
Lancelot