From your homepage, click on the right-side menu where it says Online Chess, then once on this page, look again to the right-side menu and click where it says Start New Game:
Near the top of the form, where it says 'Start a new chess game ... with,' you need to choose 'game options I select' on the drop-list. That will open up a group of new options as shown below.
On the first menu that appears under 'game options I select,' change the setting from 'Standard Chess' to 'Chess960.' The chessboard diagram to the right should now show a large question mark:
That's it! You may configure the other options as with any game.
keywords; 960, Fischer Random, Fischerrandom, chess960, shuffle