Google have released the Chromecast Android App to the Play Store for setting up and configuring all the Chromecast devices in your home.
In order to use your new Chromecast device, it needs to be set up using the Android app. The app will configure your Chromecast to work on your local network and give you an interface for managing its settings, such as changing the device’s name or inputting a new WiFi password.
Once your Chromecast device is set up, there should be no further need for this app, since the Cast button in each media app is used to stream content to your TV.
So while you’re waiting for your Chromecast to arrive in the post, be prepared and grab the Chromecast App from the Play Store!