This document will tell you in broad strokes what you need to do to create a driver in Monado. Like the many ones already in there Drivers. It is not a step by step guide to making a driver. Also what you need to do can vary a lot depending on the type of hardware you are adding a driver for and the level of features you want.

Map

The first components you will be interacting with is Prober and device management code find the hardware devices and setup a working system, along with the Auxiliary code that provides various helpers. You can look at other Drivers on how to start.