Getting started is a simple process of navigating your browser over to gaming.youtube.com and following the steps in a setup process (that includes phone verification). You'll need to set up encoding software, fill out the necessary info for your stream and tick off any optional features. There's a checklist right there on the setup page, but Google also put together a more involved guide to getting set up.
YouTube Gaming supports streaming from PlayStation 4, Wii U and Xbox One consoles, provided you've got a capture device sending video from the console to your computer. Google specifically calls out Elgato's HD60 as a YouTube Live Verified device, but there's a good chance that other game capture solutions work as well. If you've got one, try it out before you run out and buy something new.
For our current stats, we have 1.5 million broadcasters (11K Partnered channels), 100 million viewers per month who watch 106 minutes per person per day on average, and 38 million installs of our mobile app with 4.7 billion minutes watched across 10.3 million unique devices.