If you have a smart TV
1) Make sure your iOS device (iPhone or iPad) is connected to the same wifi network as your TV
2) On your iPhone or iPad, swipe down from the top right corner of your screen to access your control centre. Tap "screen Mirroring" and select your TV or casting device (e.g. LG TV, Roku stick, or Chromecast) from the list.
If that didn’t work / you don’t have a smart TV.
If you have an Apple TV box you can cast from your iOS device to your TV, even if it’s not a Smart TV
If you don’t have an Apple TV box you can still connect your iOS device to your TV manually with an HDMI cable. Depending on the make and model of your TV, you’ll likely require a Type A HDMI cable, along with the right adapter to connect to your Apple device.