What is the meaning of $_REQUEST['page'], and this line
$total = $GLOBALS['pager_total_items'][0];
in Drupal 6?
What Phil has given is with respect to the normal php.
In the context of Drupal however they have a different meaning.
In Drupal if you are trying to create a listing with the pager, the $_REQUEST['page'] is set to signify that it is a pager display, and the value signifies the current page number you are viewing.
So if you assume that there are 10 items in a every page, you can use something like
if($_GET['page']){
$first_in_this_page = ($_GET['page']*10)+1;
}
to get the number of the first item in the page.
And I think $_GLOBALS['pager_total_items'][0] can be used in place of 10(that is number of items in a page) However I am not sure about $_GLOBALS['pager_total_items'][0], but I am sure about the first one.
$_REQUEST['page'] retrieves the value of the "page" item in any of the $_GET, $_POST or $_COOKIE super global arrays, whichever provides a hit first (in PHP 5.3, order depends on the request_order directive).
$_GLOBALS['pager_total_items'][0] is referencing a potential global variable $pager_total_items that appears to be an array. The [0] is referring to the first item (or first character if it's a string).
Presumably, these variables are set / populated elsewhere. I can't provide anything relating to the drupal context.