As @invadersquibs pointed out, you need to add the plugin to a dashboard by creating a panel and selecting it from the Visualization section in the panel editor.
I believe it’s described in the tutorial already (Step 5):
Next, you’ll learn the basic workflow of making a change to your panel, building it, and reloading Grafana to reflect the changes you made.
First, you need to add your panel to a dashboard:
- Open Grafana in your browser.
- Create a new dashboard, and add a new panel.
- Select your panel from the list of visualization types.
- Save the dashboard.
Now that you can view your panel, try making a change to the panel plugin:
Is there anything we can do to make this clearer?