How does the Prepaid Commuter Benefits Mastercard work?

I currently have $210.50 on it and I’m planing to purchase an unlimited monthly metro card today. Do I go to a MTA kiosk and purchase the unlimited monthly metro with this Mastercard? Or do I purchase it online somehow?

I was told that you can tap and go with the actual prepaid Mastercard, and now I’m more confused. Thanks if anyone can help.