Service hooks let you run tasks on other services when events happen in your Azure DevOps projects. For example, create a card in Trello when a work item is created or send a push notification to your team's mobile devices when a build fails. You can also use service hooks in custom apps and services as a more efficient way to drive activities when events happen in your projects.
Note: Service hook publishers define a set of events. Subscriptions listen for the events and define actions to take based on the event. Subscriptions also target consumers, which are external services that can run their own actions, when an event occurs.
Reference:
https://docs.microsoft.com/en-us/azure/devops/service-hooks/overview

In Visual Designer you enable continuous integration (CI) by:
Select the Triggers tab.
Enable Continuous integration.
References:
https://docs.microsoft.com/en-us/azure/devops/pipelines/get-started-designer

https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions
"We strongly recommend that you include the version of the action you are using by specifying a Git ref, SHA, or Docker tag. If you don't specify a version, it could break your workflows or cause unexpected behavior when the action owner publishes an update. Using the commit SHA of a released action version is the safest for stability and security. If the action publishes major version tags, you should expect to receive critical fixes and security patches while still retaining compatibility. Note that this behavior is at the discretion of the action's author. Using the default branch of an action may be convenient, but if someone releases a new major version with a breaking change, your workflow could break."

Multi-stage builds are a new feature requiring Docker 17.05 or higher on the daemon and client. Multistage builds are useful to anyone who has struggled to optimize Dockerfiles while keeping them easy to read and maintain.
References: https://docs.docker.com/develop/develop-images/multistage-build/