Apply the yaml files in "k8s-commands.md" to you cluster, following the order of the files. If completed successfully, there will be "mongodb" and "mongo-express"pods running in the cluster.
In case of port conflicts, it is possible to connect to mongodb and express using port-forwarding into the svc of express: kubectl port-forward svc/mongo-express-service 8082:8081.
Mongo-express can be accessed at localhost:8082.