Getting started with GitLab CI/CD: stage/job/script confusion

Link the doc and describe what is wrong with it.

https://docs.gitlab.com/ee/ci/quick_start/

The page talks about the three stages of a pipeline. Then it goes on and gives an example with two jobs. Then the script step in a job is discussed. Stages are no longer discussed on the page. What is the relationship between a stage and a job?