From the little I know about ngSpice in KiCad, you have to enter voltages for your voltage sources, and you also have to specify which sort of simulation to run in KiCad.
This may be a better place to start. I have not ran any of those examples myself, but I assume you can just open them and run them.
I also noticed your schematic has the old .sch extension, which is for KiCad V5.
The most current KiCad version is V6.0.5 and you can get it for free from the KiCad website: