Vasalva makes some good points.
This is not the same for everybody, but if you are overweight and young, starting a regular hypertrophy routine that sees you in the gym for an hour, 3-4 days a week is going to assist you to lose fat, while building muscle at the same time. As long as your diet is in order
As always, diet is essential here. If an overweight person can keep their calories at the same level as they always have been, effects will be slow and difficult to see right away. And of course, if the individual is eating a crappy diet, results of any kind will never be optimal.
But with a high protein, low carb, properly calculated diet, a beginner can see quite dramatic results in terms of losing fat and gaining muscle simultaneously.
Losing fat and gaining muscle at the same time is called 'beginner gains' for those with less than a year or so of training and/or who are young. When veterans and oldies try and do it, it's called 're-comping' and it's a slow, steady process where - once again - diet is absolutely key.
Hope this helps.