Here's an example of how you'll do it day by day.
Firstly count the calories you eat throughout the day and track it using
You can read nutrition labels and measure your food with a food scale. If the food doesnt have a nutrition label then you can find out roughly how many calories it has (slice of pizza for example) by looking it up on myfitnesspal or google.
Now that you are tracking your calorie intake you need to know how many calories you will burn from exercise today. Lets say you went to the gym and you did 30 minutes of cardio with an average heart rate of 150 beats per minute.
Using the calculator for cardio in the exercise section of this cheat sheet you can find out that you burned around 284 calories from that work out alone.
Now lets say you also walked for about 30 minutes today. You would use the walking calculator and punch in the numbers which comes out to an additional 125 or so calories.
So in total you burned 409 calories from exercise today. Now add that to your baseline of 1650 for a total of about 2059 calories burned.
Lets say you ate 1400 calories today. So you ate 1400 calories and you burned 2059 calories. Minus 1400 from 2059 to find your calorie deficit of 659 for the day. Meaning you burned 659 calories of fat today.
There are 3500 calories in a pound of fat. If you burn 659 calories every day for a month you will lose a bit more than 5 pounds of pure fat a month (along with additional water weight).
659 x 30 = 19770/3500 = 5.6 pounds of fat loss a month.