The internal API is what you are using with every action you do inside the UI of the caisy app. For example creating blueprints, documents. Every single action that is happening in the app is a graphql request against the internal api. You can inspect what is going on with an chrome extension like graphql-network-inspector
How to query, and mutate data using the External GraphQL API.
When you are consuming images from caisy you relay on the asset api. It is responsible for uploading and serving assets.
The Asset CDN lets you resize your images on the fly and deliver them in the best supported format