Docker containers from the command line

A lot has been written about Docker, and most of it is complicated. I will try to write about it too, but briefly, in simple language, and with plenty of examples. The material is aimed at those who are not yet familiar with Docker.
Scheduled Backup of a Folder to the Cloud

How to set up scheduled folder backups on a server, save them to the cloud, and automatically delete backups older than 30 days.