You need to connect your Chromecast device to your telly via the HDMI or USB port, and select the correct input and wifi connection, ensuring that your telly and your device are both using the same wifi connection. You will also need to make sure you’ve downloaded the Google Cast app onto your device.
Take a look at this helpful set up site for detailed set up instructions: https://support.google.com/chromecast/answer/6006232?hl=en-GB
