If you are just beginning to use a treadmill, it may take a while to get adjusted. Once you step onto the belt and slowly increase the speed to the desired level, be sure to keep your eyes looking straight ahead because your feet tend to follow your line of sight. Also, if your goal is to burn calories, do not hold on to the handrails for more time than is necessary for you to get your balance. Letting go and swinging your arms naturally takes more energy. Moreover, as you repeat your treadmill exercise regimen week after week, you should know that your body will adapt to the pattern, making exercise less challenging. Therefore, try changing the speed and incline.
P.S. Before using a treadmill for the first time, familiarize yourself with the placement of the emergency stop button and know how to use it.