While the Prometheus UI is good for exploring the metrics and checking the state of Prometheus, it isn't the right tool for for visualizing and graphing time series. For this, Grafana is the de-facto solution.
Install Grafana on your system following the instructions from the official documentation.
Go to http://localhost:3000/ to access the Grafana UI.
Configure the Prometheus datasource pointing to http://localhost:9090.
Exercise: Create a dashboard displaying the CPU, RAM and disk usage metrics.