Is there docs for init Flow of loading .php and Functions pass vars?

Ya its a Sloppy Title

So, is there documentation regarding the Order in which files in the distribution are loaded into the page and the order in which the Vars are passed back and forth between the different .PHP pages passing Jquery and Ajax through Functions?

Like, 1st this loads, and then this is called, and a check is done here, and passed back to here, and then a DB call is done, and it returns blah blah.

Any flow info is great as I am re-writing a lot of the code and having trouble at points following the procedure threads.

Thanks Dave