Sanding may be simple, but it's an extremely important step in any woodworking project. Sandpaper is categorized according to the number of abrasive particles per square inch of paper. The larger the number, the more particles—and the finer the sandpaper. The smaller the number, the rougher the sandpaper will be and the more it will sand off the wood's surface. Make sure to sand with the grain, not against the grain. You'll know you're done when it's smooth to the touch.