TDEE is Total Daily Energy Expenditure. A good calculator (and explanation) is here:
https://www.calculator.net/tdee-calculator.html
Essentially it’s how much energy you burn on a typical day. A commonly recommended daily deficit is 500kcal or 2000kJ to lose weight at a rate of 1 pound or 0.5kg a week.
So my TDEE is 1900kcal and to lose weight my caloric intake should be 1400kcal a day.
A lot of apps help you figure out how many calories you should eat to lose weight. Based on your age, height, current weight, and activity level it tells you how many calories you need. Then it or you can deduct 500 calories per day to lose roughly 1lbs a week. I use the Lose it app.