To breed two cats, go to the male cat's page and click on "breed". This link will only appear if you are the owner of the male, or if he is available for stud. When using a stud, you will be charged the stud fee the owner has set. In case the stud option was set to "private", you first have to wait for your breeding request to be approved by the owner, and then go to your "stud requests" page and click "breed".
If the breeding was successful, your female will be pregnant for two virtual months (two real days). During this time, you should care well for her -- she will eat more than usual, and if she gets too sick, there is a chance she might lose the kittens!
If the pregnancy goes without problems, you will see a button on your cat's page which you have to click to make the cat give birth.
Cats must be between 10 and 80 months old to breed. If a female has recently had a litter, she has to wait for 13 months before she can be bred again. You can only breed cats that are not neutered. Shy and aggressive cats might refuse to breed.