The nodes don't send telemetry data to Polkadot telemetry by default. This can be enabled by using the --telemetry-url='wss:// 0' command.

You can also check our mainnet explorer at Subscan.

To monitor other data such as network usage, CPU usage, disk usage, block production, number of connected peers, etc., Prometheus is used. Nodes by default make this data available at (but can be overwritten with allowPrometheusExt) and thus Prometheus interface can be configured to listen to that. Prometheus can be downloaded from here. Once Prometheus is running, configure as follows:

# The job name is added as a label `job=dock-node` to any timeseries scraped from this config.
- job_name: 'dock-node'
# Override the global default and scrape targets from this job every 5 seconds.
scrape_interval: 5s
- targets: ['<hostname:port of Substrate's Prometheus server.>']

Now the Prometheus UI will show various metrics prefixed with substrate_.

To visualize the above metrics on Grafana, import this Grafana dashboard. If you don't know how to import a dashboard, check here.