AutoPay will become effective on your next billing cycle. Until then, you need to pay your bill as you have been doing (e.g., by mail, online, in person).
You'll see a message on your bill when AutoPay kicks in. For instance, it will say something like, "Thank you for using AutoPay." If you don't see a message on your bill, AutoPay isn't working yet, and you need to keep paying your bill normally.