Kubernetes has the concept of namespaces to logically seperate different parts of your cluster.
To simplify working with different namespaces, it is recommend to create a separate context:
kubectl config set-context <contexname> --namespace=<namespace> --cluster=<clustername> --user=<clusteruser>
After a new context is created, you can switch to this new context using:
kubectl config use-context <contextname>
All commands you execute afterwards will apply to this context.
You can verify your current context by doing the following:
kubectl config current-context
To view all the contexts:
kubectl config view