To start using Aegis, download the compiled and minified css. Include the css in your project, and start designing. If you plan to also use the Aegis javascript plugins, then don't forget to include jQuery in your html. Aegis requires jQuery for animations and rendering advanced form elements.
So, what are you waiting for? Grab the latest version of Aegis and get going! You can also have a look at project source files if you want to customize or contribute to its development.