FloraJS has two major components, a set of classes for elements in a natural system, and a renderer called Burner to draw those elements to the DOM.
To setup a simple Flora system, reference the Burner and Flora .js files from scripts tag in the <head> of your document. Also, reference the Burner and Flora .css files from link tags.
In the body, add a <script> tag and create a new system. Pass the system a function that describes the elements in your world.
You should see a block fall and bounce off the bottom of your browser window.