Build and Deploy to GKE - Missing kustomization file ‘kustomization.yaml’

I’m using GITHUB Action to build and deploy to GCP. The Deployment fails on this step with the Error Message - Missing kustomization file ‘kustomization.yaml’.

What is this kustomization.yaml file. Can someone please give me some details.

Deploy the Docker image to the GKE cluster

- name: Deploy
  run: |-
    ./kustomize edit set image$PROJECT_ID/$IMAGE:$GITHUB_SHA
    ./kustomize build . | kubectl apply -f -
    kubectl rollout status deployment/$DEPLOYMENT_NAME
    kubectl get services -o wide

I would start with the kustomize documentation Declarative Management of Kubernetes Objects Using Kustomize | Kubernetes