The schema has two uses in your project:
As a basis for code generation, creating various structs and methods that can be used in your project to communicate with the replication server.
As a description for the Replication Server, telling it how the data in your project looks like – to receive, store, and send this data to its clients.
When using MonoBehaviours and CoherenceSync you often don't need to interact with the schema directly.
If you're writing your game using ECS/DOTS you will have to create and modify it yourself. Here's an example of a small schema:
To learn more about the types and definitions available in a schema, see the specification.