Calorie Deficit. What's that you ask? Well it means you keep your calorie count below the number of calories you burn in a day.
There is something called your Basal Metabolic Rate or BMR. This is how many calories you burn in a day in rest mode. Add exercise and you burn more calories.
For example if your BMR is 2,000 calories per day you'd want to keep your intake to about 200 calories below that or 1,800 calories per day. This does not mean you can go eat one big meal of a burger and fries and a piece of pie and be done. While it may sound good in the moment, your body needs healthy fuel.
Your best bet is to include a diet full of healthy proteins, fresh plant based food, healthy carbohydrates, and healthy fats.
It really is that simple: calorie deficit in a healthy way. And guess what? If you add exercise into the equation you get to add more calories.
A little note: be sure to have protein in every meal. The higher the protein content the more satisfied and less hunger you will have.