Plug the Chromecast into your TV, connect the power cord, turn on the TV, and switch to the proper HDMI input setting. Next, download the Chromecast app on your iPhone or iPad, and while it is installing go to Settings, turn on Wi-Fi, and connect to the Chromecast option.
Then, how do you cast from an iPhone?
Make sure that your iOS device and Chromecast are connected to the same Wi-Fi network. Open an app such as Netflix or Youtube, which supports Chromecast. Load the video you want to cast. Tap the Cast button, a square with three curved lines like the Wi-Fi symbol coming out of the corner.