Go in repository Settings and rename as yourusername.github.io which is the new address of your site.

Edit _config.yml file:

name: trasparente
title: trasparente homepage
description: Can be anything

# CSS THEMES in folder /assets/css/
css: [ 'base.css' ]

# SCRIPTS in folder /assets/js/
script: [ 'jquery-1.10.1.min.js', 'base.js' ]

name and description are used for page title meta tag (along with specific page title) and in site header.

Here you can add custom css and js files you need to call across site, place relative files in assets/css/ and assets/js/ folders.

Accordingly you can edit the repository description.