Understanding a CircleCI config.yml

CircleCI reads its configuration from .circleci/config.yml. The file declares a version (2.1 is current), a set of jobs, and a workflows section that ties the jobs into an execution graph. Each job runs inside a container you specify under docker, and its steps always begin with checkout to pull your code, followed by run steps that each carry a name and a command.

The workflow lists which jobs run and in what order, so a build job can fan out to parallel test jobs or fan in to a deploy. Because steps are named, the CircleCI UI shows exactly which command failed. The mental model is small: jobs run in containers, steps do the work, and workflows decide the order — everything else is detail.