Php – What are the PHP web server architecture components and the purpose of each one of them

The trick to understanding a large code base is to not try to understand all of it. After a certain size, you can't hold a mental model in your head of the entire thing. You start with an anchor point that makes sense for whatever task you need to work on first, then branch from there, learning only the parts you need and trusting that the rest of it works as advertised. It's just like understanding recursion. If you try to hold the entire stack in your head your brain explodes.

Grep, debuggers, and intellisense are your friends here. If you don't know how a function ends up getting called, set a breakpoint on it and work your way down the stack trace.

The other thing to note is that large code bases don't spring up out of nowhere. The larger it is, the more programmers there are with experience on it, so ask them where to start, but be specific. Ask questions like, "I need to add a new payment provider. Where in the code should I be looking?" Focus on just that task instead of trying to understand the entire code base, and piece by piece your familiarity will grow.