If you are starting fresh, 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.
Adding / editing content
The contents of the index-page may be changed by editing your content/_index.md-file.
You can add a new page via running
hugo new my-new-page.md
You can add a new blog-post via running
hugo new blog/my-new-post.md
Adding your branding / colors / css
Add a custom_head.html-file to your layouts/partials-directory. In there you may add a <style>-tag, or you may add a <link>-tag referencing your own custom.css (in case you prefer to have a separate .css-file). Check out the style.html-file to find our which CSS-styles are applied by default.