Solar cookers can be built out of cardboard boxes, umbrellas, or automobile windshield sun shields, to list only a few of the options. They can be used for camping, cooking in emergencies, or routine meals at home.
Cantina West Enterprises offers a website that encourages you jump right in. It is a practical entry point for purchasing or building your own solar cooker. https://www.solarcooker-at-cantinawest.com/buildingasolarcooker.html
If you are interested in the history and science behind solar cookers, Wikipedia is a good place to start. https://en.wikipedia.org/wiki/Solar_cooker
For teachers, and adults who love details, the Solar Education Project offers extensive information. https://gdsnonprofit.org/lessons-experiments-more
The Sun Oven site also offers helpful links to educational resources.
https://www.sunoven.com/educators-resources/
Do people really do this? See to believe; here is a Wikipedia photo of students studying solar cookers.
https://en.wikipedia.org/wiki/Solar_cooker#/media/File:SOLAR_COOKER_001.JPG