The console is an in-browser command-line terminal whose shell context is a running container instance for a given resource.
This is useful for diagnostic purposes; by running commands in the console, you can see the active processes that are running inside the container, browse its local file system, monitor resource usage, observe system logs, and more.
However, because container environments are designed to be ephemeral, the console can not be used as a means to make any permanent changes to your app or the files in the container, because such changes do not persist when that resource is redeployed. Also, there is no synchronization mechanism ensuring that the changes you make in one container in the console propagates to any other containers running the same resource (in, say, a high-availability scenario).
The technique of logging into the virtualized environment inside a container might be familiar to those used to container workflows; you can achieve the same effect locally by running docker exec -it CONTAINER_ID /bin/bash for containers that have a bash shell. You can access the console for your resource by navigating to your app, clicking the Console tab, and selecting the desired resource.