Situation: old, used programmer just learning Linux PHP by himself. Took several hours to figure
 out simplest possible example execution. Main confusion: what example file / content goes where,
 then how to access testfile, then defining and matching several Apache file extensions (PHP,
 PHP3, PHP4).

Have two PHP books, your tutorial, your manual, and your examples. Never found explicit directions
 on where PHP content could appear (so at first associated "Hello World" attempts with browser side
 HTML.) (What I was trying was browser "open page" to access local PHP testfile.)

Your tutorial does say "server web directory", but not clearly enough (to a PHP novice) that this is the 
only place (for "Hello World".) (with access through a browser URL reference)

The last few hours were spent learning a little about Apache's AddType and LoadType, then getting
 testfile extensions to match Apache definitions (the <?php tags inside a file are apparently not
 enough to get  Apache to trigger PHP.)