For creating a Namespace, following are the steps:

1. After deciding on our desired name for Namespace, let's create it with a configuration file:

$ cat my-first-namespace.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: my-namespace

// create the resource by subcommand "create"
$ kubectl create -f my-first-namespace.yaml
namespace "my-namespace" created
// list the namespaces again
$ kubectl get ns
NAME           STATUS    AGE
default        Active    16d
kube-public    Active    16d
kube-system    Active    16d
my-namespace   Active    6s

2. You can now see that we have an additional namespace called my-namespace. Next, let's run a Kubernetes Deployment in this new Namespace:

// run a Deployment with a flag specifying Namespace
$ kubectl run my-nginx --image=nginx --namespace=my-namespace
deployment.apps "my-nginx" created

3. While trying to check the newly created resource, we cannot easily find them as usual:

$ kubectl get deployment
No resources found.

4. Instead, the Deployment is shown with a flag related to the Namespace:

// list any Deployment in all Namespaces
$ kubectl get deployment --all-namespaces
NAMESPACE      NAME                       DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
kube-system    calico-kube-controllers    1         1         1            1           16d
kube-system    calico-policy-controller   0         0         0            0           16d
kube-system    kube-dns                   1         1         1            1           16d
my-namespace   my-nginx                   1         1         1            1           1m

// get Deployments from my-namespace
$ kubectl get deployment --namespace=my-namespace
NAME       DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
my-nginx   1         1         1            1           1m

Now you can find the resource that was just created.