You can export products in your "Products" area in your E-Commerce Module.
"Export to Google Merchant Center"
See screenshot:
When you are on your products page you can export products in a couple of ways.
"Export to Google Merchant Center"
First thing to understand about this process is if you do a search on the left hand side of this area, and then click any of the export options it will only export the items from the search results. If you wish to export all of your items then you should click the "Show All" button prior to doing an export.
Will export all of the products listed from the search. It will include all fields that you have for your products. (Fields are "SKU", "Description", "Price", etc...)
Will export all of the QOH for the results listed. ( it will show the sku and QOH of that sku)
This option will export all of the items shown from the search. But will allow you to choose what fields to export. (This can come in handy if you are only looking to update pricing for example. Then you may only want to export the title or sku, and the price field. To keep the file small and easier to update)
See screenshot: