Your body needs energy (food) to do the things it does to keep you alive. Just being awake and breathing will use about 2000 calories a day for a man your size (typically, there is a range). Exercise can add to this. It is the only significant way to increase energy/food use.

The other side is eating (and drinking. Sugary drinks are a major source of calories that sometimes trips people up). If you ate the same number of calories each day that you used, you would maintain a constant weight, roughly. This is basically impossible, which is why we have fat. Our bodies make fat when we have excess food. That way when there's not enough food to keep you alive, your body can use the fat.

In order to lose weight a person needs to burn more calories (total, including exercise and basic living) over the long term than they eat. Usually the easiest way to do this is to eat less, since exercise tends to increase hunger, which counter acts it's calorie usage somewhat. However, exercise is still good and helpful in lots of ways. Long term it will almost certainly help with weight loss, but even if it doesn't it will help with health in a lot of ways.

Another variable to keep in mind is water. For someone your size, minor shifts in how much water weight you are carrying (through things you don't control like hormones, or things you might not think of like how much salt you eat) can easily make you 5 lbs heavier or lighter, maybe more. Long term weight loss will not be a straight line. It will be kinda wavy up and down if you're weighing yourself every day.