This is HTML template. To get started you need only Browser to run HTML files. Better upload files to the web server and run the site there.
If the template is opened from local file system, some functions may not work. For example, functions that required PHP – Instagram, Twitter, Contact Form.
To customize template you can edit CSS and HTML files. Also if you are developer, there are available source files SCSS, JS (ES6) and HTML (Nunjucks). All used plugins added from npm.
For each pages available blank CSS file for your customizations. See it here –