I have tried the following links
How do I launch other app from my own app in Windows Phone 8.1?
Call an external app on windows phone 8.1 runtime(not silverlight) xaml c# application
but nothing is working for me as i simply wants to launch one app for e.g. angry birds from my app using a button click.
Please Help
If the app has a registered URI, then you should be able to use Launcher.LaunchUriAsync for this. You can also find some help, here at MSDN - How to launch the default app for a URI.
Otherwise I don't think it's possible.