First, you need to specify HTTP and input the URL where your JSON data resides:
You could also add a second (third, fourth, etc) JSON API datasource with a different URL to grab, for example, weather data from a URL that returns JSON data.
If you do the above, and click Save & Test, does it work?
If yes, then the panel would look something like this:
Here is a thread where I showed some of my JSON plugin settings:
https://community.grafana.com/t/darksky-alternative/57037