Answer:
You are what you eat and many experts argue that proper nutrition counts for about 70% of what your body looks like.
Without the right sort of nutrition to support your training, you will be limited in what you can achieve. A steady, consistent and daily approach requires discipline, consistency and patience at first. Then it all becomes a habit.
When you overeat for the purposes of gaining muscle or getting fit you also gain some fat. To build extra muscle you need to eat in excess of what you currently eat and work out with weights or do cardiovascular exercise on a regular basis.
How much muscle you can gain, how quickly and with what definition is largely determined by your genetics and age. But everyone at almost any age should be able to gain some muscle and strength with weight training.
Proper nutrition is a crucial element in the muscle building process. That overeating is not a good idea if you are already overweight is surely something you already know. Get fit first.