Please make sure that the Chromecast is properly plugged into the display. Both Chromecast and display should have power and be turned on. The Chromecast should display setup on the display. Follow the on-screen instructions to properly setup your Chromecast.
If you would like a quick guide to setting up your Chromecast, please refer to this guide.
If you have issues during setup or additional questions, please refer to the Chromecast help page here.