How does chmod work when connected via ftp?

Question

linux

1. Having connected via ftp, Vasya created index.php. Vasya for index.php is the owner?
2. Petya connects via ftp (Petya has a different login) Petya for index.php group?
3. Does a person go to the admin panel or will he be the rest of the site?
4. Who is the interpreter?
5. Who does the script written in the file refer to (owner, group, user)? (To the one from under whom it was created?) Ie. if the code was written by a person who did not create this file, then the script will be executed on behalf of the group? And not the owner?
6. Do scripts and interpreter need to read write execute files and folders?
7. I.e. for the normal operation of the site, scripts need to be given the opportunity, like people, to read, write, execute?
8. Is executing a folder opening it?
9. What is folder reading?
10. Is the execution of the file its opening or the execution of the script that is written in it?
11. Reading a file is opening a file?
12. Others - this is the user of the admin panel, the site and the person who leaves comments on the site? Fills out a search form or asks a question in a search contact form?
13. If you close reading for others, will the site not be displayed in the browser at all?
Sorry if stupid questions.