The download button opens the iTunes App Store, where you
may continue the download process. You must have iTunes installed with an
active iTunes account in order to download and install the software. This
download may not be available in some countries.
From Spark Labs, Inc.:
The Spark Core companion app pairs with the Spark Core, a tiny Wi-Fi development board that makes it easy to create internet-connected hardware. The Core is all you need to get started; power it over USB and in minutes you'll be controlling LEDs, switches and motors and collecting data from sensors over the internet!This app will help you connect your Spark Core to the internet over Wi-Fi and control it without writing a single line of code! Our sandbox for the Spark Core, which we lovingly call "Tinker", will help you get your prototype or project up and running in minutes.