The simulator interface is described in the KiCad docs at
The information source for ngspice is its User’s Manual:
https://sourceforge.net/projects/ngspice/files/ng-spice-rework/44.2/ngspice-44-manual.pdf/download
What is found in the manual, is available in ngspice. However not everything is already supported by the KiCad/ngspice interface.
For people fond of learning by video, there is my Youtube channel at
For others a tutorial is here:
I have provided many simulation examples at
Simulation examples for KiCad/Eeschema/ngspice (KiCad 6)
and at
Simulation examples for KiCad8/KiCad9/Eeschema/ngspice (KiCad 8 and 9)