How to create an app to get the API of Storefront , which I can access merchant's order data ?

[Lola777]

Hopefully, we can create one app inside of Shopify, in order to help merchants to do better e-commerce services. How to create an app to get the API of Storefront, which I can access merchant's order data? Now I want store details of clients eg: product, order details, etc via storefront API. 

Really appreciate it, thanks in advance.