How can I use it with mapnik and mod_tile

[CrazyCoder4Carrot]

I've download the project to the dick and change the configuration file in the /usr/local/etc/renderd.conf. But the result is gray pic.

[ajashton]

How can I use it with mapnik and mod_tile

The short answer is you can't, at least not directly. This style is designed to be uploaded to a Mapbox.com account using Mapbox Studio Classic. You can use the icons and modified versions of the CartoCSS in your own custom style with custom data sources, but there's quite a lot of work involved in that. As-is this repository relies on Mapbox-hosted vector tiles to work.