All the advice above is all well and good still. But your ignoring the facts. Fat does not convert into muscle, despite stupid rumours and urban myths. You need to lose some weight really first before considering muscle mass if your 'chubby' and want to have a good looking body as opposed to just strength. So ignore doing strict weights for now and focus mainly on weight loss programs. Don't do too many cardio exercises either as they are designed to improve your respiration system as opposed to losing you weight, which they will do, but not as much if you stick to strict weight loss programs. Google a few, biking, treadmills are great for this kind of stuff. Once you have lost some weight, you may first want to build some muscle mass before considering to tone it up, judging by what you've described anyway. So start substituting your weight loss exercises for cardio and weight programs. For weights make sure your doing a reasonably heavy weight for you with only a few reps. The reason behind this is that it will build up your muscle mass. Then finally when you think you're at a stage that you are comfortable being muscle wise, then start to tone your muscles out. Subbing all your weight exercises with heavy and few reps, for a reasonably comfortable weight for you with many reps as opposed to few. This will now tone your muscles as opposed to making them look bigger. This whole process your trying to achieve isn't a single step that you can just keep repeating, it really is those three steps like I described above and do NOT expect results to happen overnight, it will take time, a lot of time.