zSimplex is HTML template converted for Grav by NunoPress LLC.
To install this template, just download the zip version of this repository and unzip it under /your/site/grav/user/themes. Then, rename the folder to zsimplex.
You should now have all the theme files under
/your/site/grav/user/themes/zsimplex
You can find inside theme directory the folder _demo where you can find the example contents for your site. If the theme is one-page layout copy all files inside _demo/pages into your home page folder. For the other folders follow the same name.