How does an airflow worker/dag/task know its status?

To Whom It May Concern:

Forgive me I am very new to Airflow…

How does an airflow worker/ dag/ task know it has completed when starting a long-running job?
If I use an Operator to launch a task in another process (or another container/ pod in kubernetes) how does Airflow know (or how can it be notified) that it is done?

Please answer or point me to the appropriate documentation.
Thank you!