what I am trying to do is, implement a functionality where a user send a message to one of his/her contacts in whatsapp and by clicking that message (it could have a link or something), the receiver of the message should come to my app or if the app is not installed, it should go to the link of my app in Play Store. How can this be done?
My only idea is to add an intent filter, that starts your app if the device opens a special URL (for example www.your-project.com). Have a look on this website: http://developer.android.com/training/basics/intents/filters.html
If the user has your app installed, a click on the link will open your app. Otherwise the link will be opened by your default browser.