If I go to the administrator of wordpress (pages- add new) in what file is the code that is responsible for building this page stored?
If I go to the administrator of wordpress (pages- add new) in what file is the code that is responsible for building this page stored?
If you want to modify the templates used by wordpress to display the pages, the recommendation is to study the page.php code, but if you want to create your own template you can start modifying some template. In TwentySeventeen they are in the folder: template-parts. I can not help you more with the details you share with us.