How do I integrate shopify store into existing webapp?

Hi,

In addition to our existing angular-built webapp, we would like to enhance our customer experience by permitting users to buy customized supplies from us inside their logged-in view of our website. A logged-in user would go to the store section of our site, see our product list, select a product(s), select a custom field for each product (that fetches information specific to that user), and check out. Our existing webapp is built with Angular. Any suggestions of where I can look? I have searched the help community and not found what I need.

You can use Storefront API, this gives you tools to integrate Shopify back end to custom built front ends. Many people do nextjs ecom store fronts using this.