Let's take for example someone that works at an office as this is a job most people do. The ergonomics science will first examine the workplace, then the work that has to be done and the person that will do it. This way you can adjust the keyboard of your computer so that if you work many hours you won't get any wrist problems. You can adjust your chair so that your feet rest on the floor. You can place the screen of the computer to the correct distance so that your eyes feel rested. You can also learn to keep the things you use close to you so that your body doesn't stretch to reach them.