Cats are fairly low-maintenance pets. They don't need to be walked, sleep more than half the day, and (most) love staring out windows or snuggling on laps. Give them fresh water and food as needed, a few toys, and a clean litter box, and they'll love you for life.
Clay litter is the most common and most affordable litter on the market. Though natural litter enthusiasts are outspoken about the dangers of clay litter, the ASPCA Animal Poison Control Center says that health risks are low, except in houses where there might be a dog who enjoys "cleaning out" the litter box. There are two types of clay litter: clumping and non-clumping.
Clumping clay litter is usually made from naturally-occurring bentonite clay, which is considered to be inert if ingested, and/or silica, another inert substance that is a primary component of sand. (Of note, California treats silica as a known carcinogen if inhaled.) Clumping litter works by absorbing liquid waste, transforming it into easily scoopable clumps. If scooped regularly (remove solid waste and clumps daily), it provides excellent odor control and only needs to be replaced once a month.
Non-clumping clay litter is made with various kind of natural clay, often with activated carbon to absorb odors. It works by absorbing liquid waste, but it does not form clumps so it is harder to scoop. Its odor control varies by brand and type, and it needs to be replaced weekly.
(Some people are concerned about the dust that comes from clay litters. It can be ingested when cats groom themselves and even inhaled by humans and pets. If that concerns you, choose a natural litter instead.)