A job is what runs your build process on CircleCI 2.0. It is essentially a series of steps that runs in an execution environment. Jobs are defined in your CircleCI 2.0
At the very minimum, your job needs to have an executor defined, and at least one step. Typically your job will first check out your repository using the special checkout step. Then, using run steps, you can execute bash commands to perform your building, testing, and deployments.
There are a whole bunch of special steps you can use to speed up your jobs or add other functionality to your build process. You can try using cached dependencies, saving artifacts you've created in your jobs, or even saving your test reports to see how your tests performed right on the job page UI.
While you're waiting for your jobs to complete take a scroll through all of the step options here on the docs page.