Reference:
https://docs.microsoft.com/en-us/azure/devops/pipelines/library/connect-to-azure

Explanation

You can set up a CI/CD pipeline to deploy your apps on a Kubernetes cluster with Azure DevOps by leveraging a Linux agent, Docker, and Helm.
Step 1: Create a service principle in Azure Active Directory (Azure AD) We need to assign 3 specific service principals with specific Azure Roles that need to interact with our ACR and our AKS.
Create a specific Service Principal for our Azure DevOps pipelines to be able to push and pull images and charts of our ACR.
Create a specific Service Principal for our Azure DevOps pipelines to be able to deploy our application in our AKS.
Step 2: Add a Helm package and deploy a task to the deployment pipeline This is the DevOps workflow with containers:

Step 3: Add a Docker Compose task to the deployment pipeline.
Dockerfile file is a script leveraged by Docker, composed of various commands (instructions) and arguments listed successively to automatically perform actions on a base image in order to create a new Docker image by packaging the app.
Reference:
https://cloudblogs.microsoft.com/opensource/2018/11/27/tutorial-azure-devops-setup-cicd-pipeline-kubernetes-d

Explanation

Explanation
https://docs.microsoft.com/en-us/azure/active-directory/develop/app-objects-and-service-principals "When you've completed the app registration, you've a globally unique instance of the app (the application object) which lives within your home tenant or directory. You also have a globally unique ID for your app (the app or client ID). In the portal, you can then add secrets or certificates and scopes to make your app work, customize the branding of your app in the sign-in dialog, and more."