Can anyone provide a step by step process how to test Performance and load in Jmeter for Silverlight application.
Silverlight applications are often front end heavy, with little or no communication to a web service. If your Silverlight application is still heavily relying on a web service and the intention is to load test that web service, then you can run performance tests for it just like you would test any other web site. If the goal is to test the performance of the front end components, then it would be different tools and a different approach.
Assuming that you are talking about the web service, then you can use JMeter, however I'm not sure whether the recording for JMeter would work with Silverlight or not (you can try it out, or look it up). If recording doesn't work, you can use tools like Fiddler or Wireshark to capture the traffic and then create the requests in JMeter by hand.
If there is a more specific issue you're running into while attempting to test performance, let us know and I'm sure someone could answer those questions.