why i cannot go to https://ybclusters.yugabyte.com.
I want to use YBcluster for kubernetes.
Are you trying to use Yugabyte Cloud? That would be at https://cloud.yugabyte.com.
However Yugabyte Cloud is a fully managed offering and works in YB IaaS.
If you want to spin up Yugabyte OSS on Kubernetes, please follow instructions at YugabyteDB Quick start for macOS | YugabyteDB Docs. These instructions cover minikube based deploy. If you have your own Kubernetes cluster, skip the minikube cluster creation and just switch kube context to correct cluster. rest should work without any issue.