The Google Shopping app automatically syncs your products and relevant information about your Shopify store with the Google Merchant Center. You can then update your Google product listings directly from your Shopify admin.
If you want to create Google Smart Shopping campaigns from within Shopify, then you need to connect your Google Ads account as well. Learn more about Google Smart Shopping campaigns from Google Ads help. If your marketing campaigns require more customization than what the Google Shopping app offers, then use Google Ads to create your campaigns on Google instead.
Learn more about the Google Shopping app requirements. If you already use Google Merchant Center to manage a product feed or create Google Ads, then you might want to review some considerations before syncing an existing Google Merchant Center account.