HubSpot is not designed to collect or store sensitive contact data, such as credit card information, which means your store pages need to be hosted outside of the HubSpot COS. However, you can host your website pages on HubSpot and connect them to your shopping pages that are hosted on an external eCommerce platform. The store pages would live on a separate subdomain, such as shop.yourstore.com.
You can then link to the store pages from your HubSpot-hosted pages using Call-to-Actions. Some shopping cart solutions also offer the option to place "buy buttons" on your COS-hosted pages. When clicked, these buttons would bring users to the external eCommerce page to begin the checkout process.
To learn more about integrating your eCommerce shopping cart with HubSpot, check out this article.