I'd agree, I think you are lightly active too.
You pretty much have it. As I understand it, the BMR is as you say, the amount your body needs to perform essential functions to stay alive (breathing etc) before accounting for any movement at all. Which is not to say that if you eat less than your BMR on any given day you'll die 
but your body would need to start depleting its stores to replace the energy you are not gaining from calories. Generally it is not a good idea to eat less than your BMR consistently over a long period of time (fasting types diets where you eat less than BMR one day but then eat 'normally' the next few days seem OK), unless you are doing a specific VLCD (very low calorie diet) prescribed by a doctor or GP.
TDEE is your BMR plus an amount on top to account for exercise - which is why the activity categories are a bit of a guess and will fluctuate slightly day by day depending on your activity, and everyone's body metabolises at slightly different rates so unless you have access to some lab testing equipment it will be a bit of a guess. If you knew you TDEE was 100% accurate and you ate exactly that number of calories every day, you will maintain your current weight. If you eat less you will in theory lose weight and if you eat more you will gain (again talking over a period of time here not day to day fluctuations).
Most calorie counting diets and apps work by working out your TDEE, then subtracting an amount (depending on how quickly you want to lose weight), to give a daily 'allowance' which is somewhere in between your BMR and TDEE, the bigger the subtraction the quicker you will lose weight in theory but the harder it is to stick to long term.
Do bear in mind that as you lose weight both your TDEE and your BMR will reduce (bigger bodies take more energy to maintain) so particularly if you have a lot to lose, do make sure to update every so often 
Good luck!