For authentication, you could rely on the default application credentials that are present within the GCP platform (GAE, Cloud Functions, VM, etc.). Then you could just run the following piece of code from the documentation:
const {Storage} = require('@google-cloud/storage');
const storage = new Storage();
const bucket = storage.bucket('albums');
const file = bucket.file('my-existing-file.png');
In most circumstances, there is no need to explicitly use authentication packages since they are already executed underneath the google-cloud/storage package in Nodejs. The same holds for the google-cloud-storage package in Python. It could help to look at the source code of both packages on Github. For me, this really helped to understand the authentication mechanism.
When I develop code on my own laptop, that interacts with google cloud storage, I first tell the gcloud SDK what my credentials are and on which GCP project I am working. I use the following commands for this:
gcloud config set project [PROJECT_ID]
gcloud auth application-default login
You could also set DEFAULT_APPLICATION_CREDENTIALS as an environment variable that points to a credentials file. Then within your code, you could pass the project name when initializing the client. This could be helpful if you are running your code outside of GCP on another server for example.