At the moment, when you want to add a container there are 5 elements that you can parametrize:
Required or not
The name of your container
You can either build your container from a Dockerfile or use a Docker Image
Configure the port of your container
Environments variables to parametrize dynamically your containers
CPU and Memory limits of your container
Check the following pages to get more informations on some of those fields:
Jobs can for instance be used for migrations, data provisioning or to create an admin.
The configuration process is close to the configuration of a container.
Select when the job will be deployed :
Before the deployment: that means after the deployment of the dependencies, but before the deployment of the containers
After the deployment: after the deployment of the dependencies and of the containers.