Walking on the treadmill will help cut down the excess fat from all over the body. That works on the cardio vascular respiratory system. The treadmill is an excellent option for walking and has the benefits of variations that you might not find in the outdoors. Firstly it works just as well when you can not access the outdoors for reasons like the cold or pollution. Secondly, you can time your walk, use the motorised treadmill to increase your pace and keep a tab on the exact number of kilometres/miles you have walked. What it can not do, however, is give you the exact caloric loss (unless you have one where you can enter your weight). The duration and speed would depend on your present fitness level and your goal. For fitness benefits, even a small 10-20 minute walk on it can make a difference, but if you are looking to lose weight, you may want to spend more time on it. As long as you are comfortable on it and can slowly increase the speed over time, you are doing well and benefiting from the exercise you are getting.