This offer is only for those with a Kindle with Special Offers (including any Kindle Touch or Kindle Keyboard that opts in to Special Offers, but not the Kindle Fire with Special Offers):
30% Off Select Kindle Accessories
Click on the offer, then click on the link on the offer page sign up and you'll get an email(right away) with the promotion code. This offer is good for one book and only one per account (if you have multiple KSO devices, they need to be registered to different accounts before you sign up to get the promotion code emails; every Kindle on an account gets flagged when you sign up for the special offer and they will all get the same code for that promotion from then on). Sign-up for this offer expires October 28, 2012, and the promo code must be used by November 4.
The email will contain a link to the promotion page. You'll need to add the items you select to your cart, then use the full check out process and enter the Promo code on the summary page (it's not automatic, like the Kindle Fire promo and you can't use one-click and get the discount).
There are a number of sleeves and covers on the promotion page, along with an A/C charger plug at 50% off the $19.99 list price (so, you would get an additional 30% off the $9.99 sale price), which you may need if you've bought one of the current Kindle models (which no longer comes with a A/C charger). Unlike the Fire promos, this discount works a single time on a single order - but you can add a couple of covers and a charger plug or two the same order before you checkout.