As with all pets, cats require love, proper care and medical attention throughout their life, which can be potentially anywhere from fifteen to twenty years.
Cats do require annual vaccinations and will require regular worming (usually every six months). If your cat gets sick you need to ensure it receives proper medical attention - cats get sick just as humans do, so plan for it. The most sensible thing to do is to shop for a pet insurance plan from a reputable pet insurance company; this will certainly help towards paying for the cost of serious illness or treatment in the event of a pet emergency.
If you are going away on holiday ensure that your cat is well looked after whilst you are away. This includes regular feeding and general checks on the well being of the animal. Cats are very territorial animals, so if at all possible it makes sense to let them stay within your home. If you haven't got someone that you can ask to help out with this task then you will need to think about finding a cattery for your pet.
Before buying a cat you will need to think of all the above and make sure that you can handle all of these responsibilities -- f you can't then a cat is not for you. Oh, and don't forget to budget for the necessities either, like cat food, litter, treats and bedding. You'll have to learn where your local pet shops are.
They will also need lots of love and affection and time spent with them for playing, grooming and making a fuss.