Download the files in a folder, open the folder in your code editor and type
npm install
Change the partials as you need it and place all the css in the sass file called inline.css.
Open the browser on localhost:3000 and voila.
The final build will be inside the "dist" folder.
The data.json file is placed in the "dist" folder as well and the tags in the html file just in case you need to build an email template with dynamic content. You can delete it if you wish.
Some email platforms allow you to use dynamic content for emails.
Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.
Please make sure to update tests as appropriate.