There are the per-domain endpoints that you can use to control and access your data using the Shop API.
This provides what you need to manage carts.
This provides what you need to manage carts as a tenant Admin.
This provides what you need to manage orders.
This provides what you need to manage Subscription Contracts.
This provides what you need to manage Customers.
Gives you the ability to acquire and release lock.
Read the documentation to learn how to use the API.
https://crystallize.com/learn/developer-guides/shop-api