ESP32 pinouts on Adafruit 8266 Huzzah, what are they?

[robwlakes]

I have had considerable success in setting up a web server on my ESP32 8266 Huzza from Adafruit. It reports back on my home brewing system remarkably well with temperatures, coupled with switching the thermostats, reporting duty cycle for the heater and on the interval between bubbles on the air lock.
However I would like to add a piezo transducer to the system so that it beeps every time a bubble escapes (the web page successfully reports the duration between bubbles). The bubble detector and one wire temp sensor work fine, but I just can't seem to find the pins that I can toggle to produce a beep from the piezo. I can't see how I have the most complicated parts working first, and cannot find the Arduino pin number to toggle to produce a simple beep.
This is Adruino 101 stuff, grrrrh.
My question is, does anyone have a definitive document or explanation on how the I/O bits on the ESP32 Huzzah correspond to the Arduino port numbers and how to use them? I can't believe I have got this far without it. It is driving me mad, I want to go just one step further and I am hitting brick walls. I have seen about 3 different Pin maps for the Huzzah, none of which have solved this problem, and that includes the ones from Adafruit. They don't specifically claim to be 100% Arduino IDE compatible.
So, a cry for 'help' please.