You will find the "Export to Quickbooks" area under YourDomainName.com > Modules > Ecommerce: Products (mX) > Orders > Export to QuickBooks

You will need experience importing to Quickbooks in order to use this feature.

Once you are there you will want to map relevant fields from users to the relevant fields in Quickbooks.

see screenshot for examples:

Once the fields are mapped you can click "Save".  And then you can click "Export".  This will create an .IIF file that can be imported into quickbooks.