First you need to understand
what is a calorie deficit.
Initially, it will be hard to follow if you have a habit of overeating.
So basically, you calculate your calorie deficit using a
calorie deficit calculator and try not to eat more calories than how much the calculator told you.
The hardest part is to stick to it during first week.
But, gradually the urge to eat extra calories will wear down. You just have to trust the process.