Upload all three files to the main root of your site. (ad_logic.php, display.php, _ad_file.csv)

Change the permissions for _ad_file.csv to READ and WRITE
    chmod 666 _ad_file.csv

Include "display.php" where you wants the ads displaying, using php you can do it like this:

<? include ("display.php"); ?>

Other Documentation

Server Side Includes
FAQ

Script can not be included in an IFRAME, ads must appear in the body of the document.