Confused on BMR and TDEE?

I'm sorry if this has been covered a zillion times, but I am confused on something. I really, REALLY want to lose weight and become healthier. My eating habits are atrocious, even since joining MFP. I haven't had a chance to get to the store and start buying veggies, fruits, and healthy things to snack on (and cook). With that being said, I feel that my best chance at weight loss is to understand how my body works....I've read some threads and I just don't get it. I'm 5'4 and about 176 pounds. My goal weight is 135. I looked up my BMR, and it is 1593. My TDEE is 2470....but I have no idea what that means I understand the BMR: that is basically the amount of calories my body needs just to function. So, if I want to lose weight, shouldn't I eat less than that amount? Where does TDEE factor in? As for exercise, I am currently doing the 30 Day Shred, and after 30 days will continue to do a routine 2-3 times a week coupled with some kind of cardio (either Billy Blanks or cardio dance). I am just so scared of NOT losing, and become overwhelmed with changing my habits. Please explain?