I am brand new to Shopify and am looking to use it as eCommerce platform for my business. I have already built a website on Squarespace, and wonder if the two are able to connect - so that Squarespace would be the front end of the website and Shopfiy the back (payments, manage inventory etc).
This is a great question, I definitely understand the desire to keep an existing online store.
Shopify and Squarespace are technically competitors in the ecommerce industry so there is limited compatibility between the two platforms. That being said, you should be able to use Shopify’s “Buy Button” sales channel to create and embed products and collections in an external website, including Squarespace. You can check out more info on the Shopify Buy Button in our Help Center here: Shopify Help Center | Creating a Buy Button.
This process will limit some of the options for apps or extensions on the cart or checkout page. So upsells and things like that might not be supported or be less successful.