Hi rick! Sorry for the late reply (didn’t get notifications for some reason - need to check if the forum is working ok)!
The RTMP streaming option was an experimental feature that will change radically in a few days with upcoming update – in other words, it will get easier to use 
Koolstorm basically laid down the whole process here, but the very short version is that you first need to get OBS or other streaming software ready, then input the given RTMP stream url and key (from the event start warmup page) and off you go.
Check out the excellent Configuring OBS for Slipmat.IO tutorial by TD, it should give you lots of details!
Feel free to ask more help if needed!