Weight training is important for toning, strengthening your metabolism, and for improving aerobic endurance. While cardio can help burn fat, if you are aiming to transform the shape of your body (bulking up or losing inches) weight training is a must. Using the wrong weight, however, is a waste of your efforts. Choosing the correct weight is essential, and here is the easiest way: Practice working out with very light dumbbells until you've mastered proper form for the exercise you're doing. For most, a 5 lb. weight is a good starting point, but even lighter dumbbells exist if you need them. Men typically (but not always!) have more upper-body strength than women, but they should still begin with relatively light dumbbells. Men should begin with weights anywhere from 5 to 15 pounds. Pay attention to how many reps you can do with light dumbbells. If doing 20 or less is a challenge, you're already close to your ideal weight for that exercise. If this is no problem for you (be sure you are actually using good form!) then you are ready to move up. There should be a bit of a challenge with each move, or you are not using a weight heavy enough for your body. I have attached a video that really explains this well!