Entry point https://github.com/kubernetes/kubernetes/blob/master/staging/src/k8s.io/kubectl/pkg/cmd/create/create_namespace.go#L76

• Complete completes all the required options
• Validate validates required fields are set to support structured generation
• Run calls the CreateSubcommandOptions.Run in NamespaceOpts instance
• createNamespace outputs a namespace object using the configured fields
• Then o.Client.Namespaces().Create(context.TODO(), namespace, createOptions) creates namespace

Next part staging/src/k8s.io/client-go/kubernetes/typed/core/v1/namespace.go