Yes you can stream with your data and there aren't any steps really. You just have to sign in with your email and password and give it permission to use your location. There is a gear icon on the top right you can tap and just make sure Stream with Mobile Data is turned on and there is also an option to change the Cellular Streaming Quality to either Good or Better, which I assume Better would use a bit more data than Good.
The question asked was about streaming from an iPhone to a TV. The iPhone app supports both casting (to a Chromecast) and AirPlay (to an Apple TV), but it isn't clear right now if either uses cell data (that is, the streaming is through the phone) or if it does URL forwarding so the TV device actually does the streaming directly. In the latter case, it would not be using cell data (at least, not "free" cell data). The last time I tried testing this using an ATV, I wasn't able to get it to work at all with the ATV's network removed (implying the ATV was doing the streaming), but I didn't devote much time to the effort. To actually do the casting/AirPlay is straightforward - assuming the TV device is set up and visible to the phone, and you have the app running and displaying a stream on the phone - there are icons for casting or AirPlay in the upper right corner.
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