Navigate to the folder your script is located. You can use ls to list Folders and Files, and cd to change directory.
After you are in the correct folder, type node . or node [filename].
Example: node variables.js
If you do not want to navigate folders, you can just simply type the full filepath to your script, node [filepath/filename].
Example: node JavaScript/variables.js
Alternatively you can run your scripts in the browser, using a html file that includes your script. Just drop your html file in your favorite browser and open developer tools, check the console tab to see the results.