If you are using a newer version of QuickBooks (versions that allow .csv exports), log into the admin portal of your Newtek Cart installation and go to the "Database & Back-up Tools" option, which is under "Cart Settings."
You will then be able to select the data type and date range for the data you wish to export into a .csv file. This .csv file is a common format and can be used in many programs other than QuickBooks.
If your version of Quickbooks does not support .csv exports, you can use the "Export to Quckbooks" tool, instead. This option is located under "Users & Orders" in the admin area.
From this page, you can export the data into a .iff file, which QuickBooks supports.