calories

calories measure the energy content of the food you eat
if you exercise you use more energy than when you are lazying around
if the total calories you consume in a day exceeds the ones you use up,
the extra will be stored by your body, usually as fat

there are two simple choices to reduce the calories from turning to fat:
1. eat fewer calories by eating less or differently; and/or
2. burn more calories by exercising more
if you do either or both of the above, then you can see changes to your body weight

your daily calorie intake
multiply your weight in kg bt 22 to estimate your daily calorie requirement for a moderately active person who does not exercise...

for example:
my weight: 63kg
my daily calorie intake: 63 x 22 = 1386 kcal per day

how much calories you need to burn?
if you're an active person,
ie walk 10,000 steps everyday, or more
you're actually adding your daily calorie intake of your body

for example:
add 100 calories for every mile you run, jog or walk
let's take 62kg again and you run for 5 miles a day
(63 x 22) + (100 x 5) = 1886 kcal per day

if you want to lose weight,
reduce your daily calorie intake below your recommended daily calories requirement
however, for health safety sake,
do not reduce your daily calorie intake to less than 80% of your calorie requirement