Start by installing the Meteor platform if you haven't already (See reference).

Create a new project by running these commands in your command line:

$ meteor create whatsapp
$ cd whatsapp

Your app now contains a live and ready example. To run our app simply type the following on the command line:

$ meteor

We can also run our app inside the iOS simulator or Android emulator, we just need to add the platform so Meteor will build the project for the new platform: