Orchiectomy is essentially a surgical operation that removes a man's testicles.
Because the testicles are the primary source of testosterone production, removing the testicles rapidly reduces the amount of testosterone circulating in man's body.
Orchiectomy is not commonly used today to lower a man's testosterone because very effective medications now exist that achieve the same result. Surgically removing the testicles may result in a more rapid lowering of testosterone levels, however.
For men with prostate cancer, the hope when removing the testicles or using medication that reduces the testosterone level is that the prostate cancer will stop growing or markedly reduce its rate of growth. It is thought that testosterone is one of the major promoters of prostate cancer growth in the body.
Obviously orchiectomy is a major surgery, and this option should be discussed at length with your doctor(s) before going ahead with it.
Nelson WG, et al. Prostate cancer. Abeloff's Clinical Oncology. 4th ed.