Compile variables.less file to where? FLAT UI

Question

I'm pretty new to the use of .less files. I downloaded a FLAT UI bootstrap. Now I wanted to change the base color of the bootstrap and therefor I used the variables.less file. There I changed the brand-primary to an other colorscheme. Now I read everywhere I need to compile this file. But to where do I need to compile this because there is no variables.css file available only there is a bootstrap.css file and flat-ui.css file. I'm I seeing something wrong here? It's about this bootstrap: http://designmodo.github.io/Flat-UI