What is the -> for?
 

I can't find any reference to the "->" characters ... as in
[$DB_site->query_first], at either the PHP site or SQL site

what does it mean?

Hmm, afaik it has to do with the objectoriented part of php.

$DB_site is an object and -> calls a method from this object (in your example query_first)

it has to do with classes in php

Analogy: it's like . in Java/VB; it's used to access a member property or method of an object.

So $DB_site->query_first() calls the query_first() method of that instantiation of whatever class $DB_site is.

http://www.php.net/manual/en/language.oop.php

or if you called mysql_fetch_object then
echo row->foo

mind you im a bit rusty but there are a few purposes...