Bicycle wheels are made of four components. The hub is at the center of the wheel, and the rest of the wheel rotates around the hub. The rim forms the outside edge of the wheel and is where a tire is installed. The hub and rim are connected with spokes that are attached to the rim with nipples. Tension on the spokes is created when the nipples are tightened.
Normal wheels have varying numbers of spokes from as few as 8 to as many as 48. Most wheels fall into the middle of this range. The vast majority of riders should use wheels made with 28, 32, or 36 spokes with lighter riders (under 160 pounds) doing well on 28-spoke wheels and heavier riders (over 200 pounds) doing best with 36-spoke wheels. Usually, the front wheel can be built, if desired, with fewer spokes than the rear one.
Despite all the variability in brands of hubs and rims as well as their spoke count, the key to the strength and durability of any wheel is spoke tension. The best professional wheel builders will tension the spokes very highly and measure the tension on each spoke with a tension meter. This is a time-consuming process which requires skill to do it properly, but it is what mainly makes the difference in the quality of the finished wheel.