#circleci
A run is comprised of one or more named jobs. Jobs are specified in the jobs map. The name of the job is the key in the map, and the value is a map describing the job.
If you are using Workflows, jobs must have a name that is unique within the .circleci/config.yml file.
If you are not using workflows, the jobs map must contain a job named build. This build job is the default entry-point for a run that is triggered by a push to your VCS provider. It is possible to then specify additional jobs and run them using the CircleCI API.
Primary Container - the first image listed in config.yml. This is where commands are executed for jobs using the Docker executor.