Pyro is composed only of it's bundled add-ons and it's core, the Streams Platform. Documentation for each is maintained in their respective addon or package repository.
Checkout the list to the left for documentation relative to all the first party add-ons and core packages included in Pyro.
To get started with Pyro, it's structure, installation, security, and contributing checkout the PyroCMS documentation in the Core category.
To learn more about Pyro's engine, it's services, and developing with Pyro, have a look at the Streams Platform documentation in the Core category.