This is a general indicator to determine if you are in a healthy weight range. BMI does not take into account people that lift weights and have larger muscle mass. People with larger muscle mass should use body fat% as an indicator if they are in a healthy weight range.
BMI is not always accurate for people that have a lot of muscle mass, a better indicator would be to have your body composition measured. Take a look at the bodyfat table on slide 12
This is the amount of calories your body would burn to stay alive, with no activity. Your TEE (Total Energy Expenditure) takes into account thermic effect of food and activity factor. This is number you should go off of when creating a calorie deficit.
To lose weight you have to create a calorie deficit either by eating less or exercising more. For weight loss you would want to subtract 500 calories per day from your Total Energy Expenditure and this will allow you to lose 1 pound of body fat a week. You can create an even greater calorie deficit by exercising.