I can't find the "cast" icon on my iPad

You'll want to check that your TV supports Airplay so that you can stream from your device to your TV. Not all apps allow the use if Airplay so you may not be able to stream the content you have selected.

Casting is called AirPlay in the Apple world. You need to get yourself an Apple TV/Apple TV4K which will then do the needful with your iPad (or any other Apple device/computer). Costs under $200. Good luck!

Make sure you are on the same Wi-Fi Network on both devices.