We actually did an outline of what Super Chat was which can be found here
Basically SuperChat is a brand new feature that replaces fan funding, as it available if you meet the following criteria :-
Your channel is enabled for live streaming
Your channel is monetized
Your channel has >1,000 subscribers
You are over 18
You are located in Australia, Canada, France, Hong Kong, India, Italy, Japan, Mexico, New Zealand, Philippines, Poland, Portugal, South Korea, Spain, Sweden, Taiwan, Uganda, UK, USA, Germany.