Unlike some previous versions of Windows, the disk indexing in Windows 8 (and 7) is actually very efficient, works well, and does not slow down the system. The exception being if you are running Windows 8 on a low end Windows XP era or older computer. Even then it's probably not worthwhile to disable the service.
However, if you insist on losing all of the benefits for (at most) 1% CPU usage savings, then press the Windows key and the letter "w", then type "services" and select the "View local services" icon. Find the Windows Search service in the list and disable it.