By default the Blank page is the page that does not have header and footer and displays content only. We use this template to create coming soon pages, for example.
If you need page with header and footer why do you need Blank template? Use the default template.
I want to make custom page connected to theme but with my php functionality on it so I need a php file that contain functions to load full header and footer so I could add the rest inside. It is actualy default template but I cant find it in files?
Create php file in child theme with the name of the necessary template, use this name as the template name http://prntscr.com/o7hk78 and then call the header, footer and content you need. Save. After that template will be available in the list of page templates http://prntscr.com/o7hm14