https://docs.woocommerce.com/document/product-csv-importer-exporter/

Product CSV Importer and Exporter

WooCommerce has a built-in product CSV importer and exporter, as of version 3.1x.
Import, export or update hundreds or thousands of products in your WooCommerce store with a single CSV. This tool supports all product types, including variations.
  • First-time store owners get started more quickly by exporting and importing products during setup
  • Existing store owners can update tens or hundreds of products with new info or place them on sale, or sync multiple storefronts
  • Note that this importer has a bug that means it can NOT update the SKU field at all,
1/ Go to: WooCommerce > Products.
2/ Select Import at the top. The Upload CSV File screen displays.

It is very important to get the mapping correct...