# Concepts

This section explains how the high-level APIs such as `ActorBuilder` works under
the hood. We strongly recommend finishing reading *Get started* section before
you continue.

In this section, you will understand fundamental concepts of SAPIEN, including
``Scene``, ``Entity``, ``Component``, ``System``, and how physical simulation
and rendering are implemented with these building blocks.

```{toctree}
:titlesonly:

entity
lifecycle
```