php page for what is displayed to the customer calls many the rest of the typical html structure from pages in the includes folder to "design"/ layout the customer facing pages.
/includes, header.php, left_column.php, right_column.php, footer.php, application_top.php, Checks ssl, database file, set cookie use, IP address, application_bottom.php, same as application_top.php, configure.php, filenames.php, /functions, general.php, will call tables from the database i.e. "PRODUCT_NAME", /classes, order.php, /modules, shipping.php, order_total.php, payment.php, /boxes, Individual .php pages for each information box on the page. Code determines how & what to display on the page, /languages, english.php, contains "variables" that are used in the php and defines what "text" and what language should be displayed to the customer, /english, same filenames as in the main catalog, however these just define what text to display on the page in "english" ( follows the same definition for other language folders and .php file), index.php, definition for english text on the main page, /images, location for english language buttons
configure.php, defines the URL & directory path for the store and admin. As well as the database - make sure this is secured
osCommerce Docs :: PHP Cross Reference For osCommerce 2.2 MS2