Neutering is a general term for castrating a male or spaying a female cat.
You can find information on spaying a female cat here.
Castration is the surgical removal of the testicles. Performed as a routine operation under general anaesthetic, the patient is usually admitted in the morning and is collected later the same day. We recommend castrating cats at 5 months of age.
The primary reason for castration is to prevent unwanted kittens from being produced. Other benefits include:

Entire male cats can make good pets, but the owner is never the primary focus of their lives. A male cat likes to have a home and a kind owner, but will desert all these comforts for a female or if another male enters his territory. In fact the intact male usually only comes home to eat and sleep! Castrated cats, especially those neutered at 5 months, become more docile, affectionate and playful as the owner becomes the primary focus of their lives.
Unless you want to use a male cat for breeding purposes there are few advantages and a lot of disadvantages to keeping an entire male cat.
A castrated cat has fewer medical problems, eats less, lives much longer on average and does not add to the pet over-population problem and makes a more loving and rewarding pet.
Your local Vets4Pets Veterinary Practice can give you further advice on neutering your cat. Please select your nearest practice from the list below.