Install kubectl via gcloud:
gcloud components install kubectl
Test the install:
kubectl version --client
You should see something like:
Client Version: version.Info{Major:"1", Minor:"18+", GitVersion:"v1.18.18-dispatcher", GitCommit:"de944d802c49735ad0f4bfe82ddfa19737ebe962", GitTreeState:"clean", BuildDate:"2021-05-13T17:51:55Z", GoVersion:"go1.13.9", Compiler:"gc", Platform:"linux/amd64"}
Next: Provisioning The Cluster