You can start here: New Sigmoid Scene to Display mapping
And then there’s Evaluate the new sigmoid tone mapper just merged into master ... and Sigmoid module advice and guidance needed, for example.
Both with sigmoid and filmic, the idea is that a correctly exposed image has midtones where they should be. That is your task. Then, the tone mapper is responsible for getting the other tones inside the low dynamic range of the output / display world. With filmic, you have more (direct) control (set your black and white points). With sigmoid, you have indirect control (e.g. selectively boost highlights before or after sigmoid).