What is the working principle of apache?

Question

PHP

Good day. The question is this: let's say 2 clients started loading the page at the same time. Do I understand correctly that until the first client receives a response, the second apache will not even start executing the php code?

Answer 1

Parallel execution:
A client comes, requests data (php, html, js, json - yes, whatever), the
server issues resources for it and it works,
other clients also come and receive their resources...

Answer 2

Apache spawns a) a new handler process b) a new handler thread (depending on which dispatcher it is working with). Each process/thread executes its own copy of php, and its own copy of the script.