There are a number of ways in which you can create a docker image. These include:
Copy And Commit
In this method, you copy to a container and then commit that container as an image.
For more information and detailed steps, see Copy and Commit
Docker Build Command
The docker build command builds Docker images from a Dockerfile and a “context”. A build’s context is the set of files located in the specified PATH or URL. The build process can refer to any of the files in the context.
For more information and detailed steps, see Docker Build Command
Trigger Build From A Docker Compose File
This approach calls the exact same Dockerfile mentioned above, but allows you to specify the 'Recipe' for the image in advance. For example, the resulting image name, the context and any parameters that should be used. This allows for a much faster and consistent deployment.
For more information and detailed steps, see Trigger Build From A Docker Compose File
Build and Push to Azure Container Repository
Just as you can use docker commands to build images locally, you can instead use ACR Commands to trigger builds remotely on your Azure Container Repository.
For more information on this see: Building Docker Images: Using ACR Build Command
Trigger Automated Build to Azure Container Repository
If you intend to start using docker images in production, then you need to start automating the building of your images. With ACR tasks, you can add a hook that monitors your code repository for Pull Requests or commits. This can then trigger a build and save the resulting image to your container repository.
For more information on this see: Building Docker Images: Using ACR Tasks