There are three steps to setting up your Google Product Search / Google Shopping Feed.
First, create a Google account and/or log into Google Merchant Center.
Second, configure your Google Merchant Center Settings in your Google Merchant Account.
Third, navigate in your Nexternal Order Management System (OMS) to Products/ Export/ Traffic Tools, and click the Preferences link next to Marketplace Exports. Then configure your settings and enter your FTP login credentials from Google Merchant Center.
Please make sure you have the "Upload" Input Method selected on the Google Merchant Center / Feed / Name & Input Method screen in the 'Choose an Input Method' section. (The Google Merchant Center "Fetch' input method will not work with the Google Product Search Automated Data Feed.)
Once configured, visit the Google Merchant Center Settings icon (wrench icon in the top navigation of Google Merchant Center), select the 'SMTP/FTP/GCS' option in the drop down menu, then expand the "FTP Settings section" to generate and copy your Google Merchant Center FTP Username and Password.
Copy this Google Merchant Center FTP Username and Password and paste it into the OMS (Products/ Export Traffic Tools / Marketplace Exports Preferences / Google Shopping Options/ Google Shopping FTP User Name and Google Shopping FTP Password) (and retype password field as well.)