Overview
App Manifest
The App manifest is a JSON file that describes the application details, including name and version. It lists the required by the App permissions. Defines App mounting points in the Dashboard and specify the Auth Persistence.
App Requirements
Saleor API requires two endpoints to be implemented on the App side - the Manifest URL and Register URL.
Communication with Saleor API
Depending on App needs it can communicate with the Saleor API using events based on webhooks or with Saleor GraphQL API. Check "Communicating with apps" for more details.
Auth Persistence
Saleor Apps communicate with Saleor API using token - obtained during App registration process. The Auth Persistence Layer page describes the ways you can store obtained token depending on your App needs.
If you're building a single service dedicated only to your shop, check Webhooks section of Extending dashboard as it may handle all your needs.