It's not hard, you just have to know where to look. Roll your cursor up to HOME in the upper right and select Online Chess. Click on Start New Game (don't worry, it won't immediately start a new game). We're getting close now. Just above the big orange button you should see "standard" and a little upside down triangle. Click on the triangle to reveal a drop down menu and Voila', Bob's yer uncle, there it is: Chess 960. Enjoy!
how to play 960

I did all that and found what you guided us to do but then got an error message that said
Oops?! We noticed the following errors in your form
Your Rating range must include your own rating. Try lowering your minimum or increasing your maximum range.
But there is no fields for that, that I can see.
Do you know?
Thanks
the only way i found is to click play > 960
but this send me to the normal differed game, i found no option to make it 960
please help