That is the origianl potty seat. You remove ring by ring on the inside. It is a training aid so that eventually you will not need it at all. They will just use a normal toilet without the pottycat seat.

The following is a brief description, our included booklet has more details.

Our system involves the use of a plastic device which sits on the porcelain rim of your toilet. Your toilet seat then folds down into its normal position. Initially you will place kitty litter in the device and your cat will accept this as its new "litter box". After this step, a small hole will be cut in the center of the plastic device which the cat doesn't hardly notice. Over the few weeks of your cat's training period this hole is gradually made larger and larger, encouraging your cat to move closer and closer to the toilet seat. Your cat may immediately "perch" on the toilet which is good. Most cats will initially rest their front paws on the toilet seat as they use the kitty-litter in the device. No matter how "advanced" your cat is initially, it is recommended that you start with a small hole in the middle of the device and slowly make this hole grow. Eventually the hole will reach the perimeter of the device and you can remove it permanently! You now have a potty-cat.

Our instructions will detail many bits of advice which will ensure that this process is very natural and easy for your cat.
directly from the site