The Arduino library was developed to optimize firmware development, and to simplify the process of creating IoT devices
To install the library, you can use Arduino Library Manager and search for OpenDevice (se more details guide)
The best reference to learn is to read the examples, for advanced features and a more complete code see example: Projects/AcessControl
To better understand some peculiarities of the source code, take a look at: Firmware FAQ
Sources: https://github.com/OpenDevice/opendevice-lib-arduino
Here you will find the documentation generated automatically from the sources:
http://opendevice.github.io/opendevice-lib-arduino/annotated.html
https://github.com/OpenDevice/OpenDevice/wiki/Supported-Devices