Containers are built via a [definition file](https://apptainer.org/docs/user/latest/definition_files.html) and the `apptainer build` command.
In the definition file you usually start with a (*base container*)[https://apptainer.org/docs/user/latest/definition_files.html#header] and build your environment on top of it in the [`post`](https://apptainer.org/docs/user/latest/definition_files.html#post) section.
In the definition file you usually start with a [*base container*](https://apptainer.org/docs/user/latest/definition_files.html#header) and build your environment on top of it in the [`post`](https://apptainer.org/docs/user/latest/definition_files.html#post) section.
The following simple example defines a container in which WandB is installed on top of NVIDIA's JAX container.
