For overall health improvements - the mental boost it provides and enhanced blood circulation etc - aerobic exercise should be included in any good fitness program, and indeed it does burn body fat and can assist weight training throughout this process. But to overemphasize it while neglecting high intensity weight training is a fundamental mistake. In fact, excessive cardio may negate our weight training efforts; it can rob us of our strength and negatively impact our recovery abilities. Yet, used correctly as a tool rather than blindly using it as foundational to the achievement of our fitness goals, it can improve recovery and enhance muscle growth: three 45 minute sessions per week would be sufficient, slightly more or less depending on the host of individual factors (metabolic response, body type and so on) that often make designing specific training programs difficult.
So how does all of this relate to fat loss or weight loss? Initially, during aerobic exercise, glycogen is used. But, in its absence or when the activity lasts a long time, fat metabolism is initiated and fat is broken down to be turned into ATP. Generally, a workout performed at a moderately high level of intensity over a long period of time will use fats for energy. But, research also shows that HIIT can activate fat metabolism as well.
But in today's unenlightened "believe everything you hear" age this most effective and proven approach, for some strange reason, does not seem to attract much interest. This is no more obvious when one witnesses the "technological" revolution that is happening within the fitness industry, where a newer even more ridiculous gadget compared to the one that preceded it promises to build you the body of your dreams, with little effort on your part, "in 30 days or your money back"; where a machine that does most of the work for you is touted as a suitable replacement for actually applying a modicum of effort. https://www.youtube.com/watch?v=mDHGaU_jGrQ