Google Merchant Center
The Google Merchant Center is a tool that helps you upload your store and product data to Google and make them available for Google Shopping campaigns and other Google services.
Shopify's Google Shopping channel asks you to log in to your Google account to sync your Shopify store with your Google Merchant Center account. If you don't already have a Google Merchant Center account, then an account is created for you during setup.
Syncing your Google Merchant Center account
When you set up the Google Shopping channel, Shopify syncs your products and relevant Shopify store settings like shipping and taxes to the Google Merchant Center.
Syncing your domain
When you log in to your Google account during setup, the Google Shopping channel checks to see if your Shopify store's domain matches the domain associated with your existing Google Merchant account. If your domain is associated with a Google account other than the one you used during setup, then your domain is claimed and will no longer be available to the other Google account.
Syncing your product feed
The Google Shopping channel syncs your products in a separate step after your Merchant Center Account has been configured. If you already have a product feed set up, then it is overwritten to avoid conflicts between your Shopify store and your Merchant Center account. For more information about managing which products are synced, see Syncing your products.