The board used in this community contribution is a STM32F411CEU6 based board from IngenuityMicro called Oxygen. The board has 20 pins for your use. The pins on the opposite side of the USB connector can be used for several add-on boards for f.e. BLE, WiFi (ESP8266).
The pins can be used for several purposes, GPIO, PWM, I2C, SPI, SERIAL, etc.
Further details how the pin out is supposed to work can be found in the resources folder, of course since we know now what MCU pins go to what PCB pins we can change the board.h depending on what you want to achieve with the board.
For more information you nay want to have a look at https://github.com/piwi1263/Molecules
Checkout the C# managed helpers available for this board.