It's pretty straight forward. When you download it, unzip the package, and open up qb_export.inc.php, set your license code and a few of the preset options, as well as your modernbill database information. Upload the qb_export.inc.php, qb_export.php and the 'ioncube' directory to your site, and browse to the page.

What settings you enter for the Income and Deposit accounts will depend on your QuickBooks setup, and you may want to gather advice from your accountant on what they would like them set to. It is modeled after the export system that PayPal uses, which should make it rather easy for your accountant to give you advice on which fields to use.

Also keep in mind that you can set those in the config file so they are the same every time.