If you purchase a new ChromeCast, you should go to the website www.Google.com/chromecast/setup set up your device first.
How to set up:
1. Click here to download the the ChromeCast app now!
2. Plug your Chromecast into your TV and change the Input (or Source) until you see the ChromeCast screen.
3. Click on the Chromecast app on your mobile phone or PC and follow the instructions to install it.
4. Once completed, you can start to enjoy Google ChromeCast.
Google ChromeCast Setup Video Demo: