To access the Monitoring UI, log in to Kibana and click on Stack Monitoring from the side navigation. If the monitoring data collection is not enabled, you will be taken to the following screen, where you can enable monitoring by clicking on the Turn on monitoring button. By default, monitoring would be enabled but data collection would be disabled. These settings can be dynamic and can be updated using the cluster update settings API, which doesn't require a restart to occur. If the same settings were set in elasticsearch.yml or kibana.yml, a restart would be required:

Once you click on Turn on monitoring, the cluster settings will update, which can be verified by using the following API:

curl -u elastic:elastic -XGET http://localhost:9200/_cluster/settings?pretty
{
  "persistent" : {
    "xpack" : {
      "monitoring" : {
        "collection" : {
          "enabled" : "true"
        }
      }
    }
  },
  "transient" : { }
}

Once data collection has been enabled, click on the Stack Monitoring icon on the left-hand side menu. You will see the following screen:

This page provides a summary of the metrics that are available for Elasticsearch and Kibana. By clicking on links such as Overview, Nodes, Indices, or Instances, you can get additional/detailed information. The metrics that are displayed on the page are automatically refreshed every 10 seconds, and by default, you can view the data of the past 1 hour, which can be changed in the Time Filter that's found toward the top left of the screen. You can also see the cluster name, which in this case is elasticsearch.