The easiest way to get started with FCG  (once you have downloaded the latest release) is to navigate to the tutorial folder, in which you find files such as fcg-manual.lisp (under fcg-manual) and fcg-demo.lisp (under grammar-writing). These files explain the basic ideas of FCG in a step-by-step manner and teach you how to edit and write FCG constructions. If you want to read up on the syntax and semantics of FCG, there is a comprehensive Wiki page on this entry on the Babel wiki.