Once you have installed and enabled the Feeds module, the next step is to create an "importer" at /admin/structure/feeds.
NOTE: This step will require that you have already set up the Vendor content type with all the recommended fields as well as the Products taxonomy vocabulary.
/admin/structure/feeds/vendor_import/mapping
Feeds Tamper
You will also need to configure the Feeds Tamper module in the following way at /admin/structure/feeds/vendor_import/tamper