You need to be covered by a TV Licence to watch or stream programmes live on an online TV service (such as ITV Hub, All 4, YouTube, Amazon Prime Video, Now TV, Sky Go, etc.).
This applies to any device you use.
You don't need a TV Licence if you only ever watch on demand or catch up programmes on services other than BBC iPlayer - and never watch live TV programmes on any channel or TV service, including on iPlayer.
Streaming is watching TV using the internet instead of downloading a file to your device and watching it later.