For more information, read the official setup guide of Hugo.
Simply copy over the contents of the exampleSite-directory included in this theme to your source directory. That should give you a good idea about how things work, and then you can go on from there to make the site your own.
You need to have NodeJS installed. Then, copy the package.json- & package-lock.json-files from the root of this theme to your site’s root. Run npm install & npm install postcss-cli postcss -g to set up your PostCSS-Pipe.
Take over main.css & tailwind.config.js
Simply copy over the assets/css/main.css-file from this repo into your local assets/css-folder. Also, copy the tailwind.config.js-file from the root of this repository to your site’s root. You may then add any CSS you like into your own assets/css/main.css-file and even overwrite the tailwind configuration in tailwind.config.js-file. See tailwindcss > docs > configuration for more details.
Optional: Take over postcss.config.js
Take full control of the PostCSS-setup by copying the postcss.config.js-file from this repo into the root directory of your site.
Start with the contents provided in the _index.md-file in the exampleSite/content-directory. That should give you a good idea about how things work, and then you can go on from there to make the site your own.