This page basically re-creates the Serenity RPG book that I have and you don’t. Summarizing the information into several groups:
Gameplay tells you what to roll for, when to roll, and what different roll results mean. Important to note: At the upper right of the screen, you’ll see a little icon with a pair of dice on it. That’s ObsidianPortal’s virtual dice roll generator. Very handy! Use it often!