Word
API
An API is the doorway one program uses to ask another program for something, without a human clicking anything.
Also called: application programming interface, the API
Your store already has one. When your shipping app pulls today's orders, it is not logging in and reading the screen, it is asking through the API and getting back a tidy list, like the order window at the back of a restaurant: a fixed set of things you can ask for, no wandering into the kitchen.
Your own tool will use your store's API to read orders and tracking numbers. The mistake is assuming an API can do everything the website can. It usually does less, and what it does is decided by whoever built it. To use one you need an API key.