Are you completely new to Cordova programming? If you visit the cordova site and follow the example step by step. On the time you create the project and try to add a platform, if you forget to navigate to the your project name directory and you set your preference platform. You will receive the following error message Current working directory is not a Cordova based project..
To fix this problem is pretty simple, make sure you navigate to the directory of your created project and re-execute the command again. See below image for more details.