# Concepts and Configuration

Where Getting Started shows what a program looks like, this section explains why. Its throughline is the two-phase model at the heart of the API: you first *describe* a scene, then *build* it once and *step* it, and almost every configuration choice is made in the describe phase and frozen at build time. Read it to understand the object model and to set backends, options, conventions, and saved state deliberately.

```{toctree}
:hidden:
:maxdepth: 1

concepts
initialization
config_system
conventions
checkpoints
```