It's an unmanaged package in Salesforce then you can customize the flow and mapping the data between Shopify and Salesforce.
Once you set your Shopify store (one or more than one), it creates a webhook for customers and orders. It means that the orders are pushed to Salesforce once it's created in your Shopify. The Shopify Order JSON contains the Customer data. So, the contact is created in Salesforce.
As the Order is not related to Contact in Salesforce, it's through Account... I follow HEDA architecture in Salesforce
This package includes two flows, one to manage the Customer integration and one to manage the order integration. You can modify it if instead mapping Shopify Order with Salesforce Order you want to map Shopify Order with Salesforce Opportunity.