New to MFP w/ FitBit

I started using MyFitnessPal with my FitBit and am a bit confused - I know that we burn calories through out the day no matter what we are doing but how accurate is the negative calorie option. For example I woke up this morning and according to my FitBit I had already burned 400 calories and it gave me an additional 190 calories on MFP.

I guess I am just confused as to if I should be eating these calories and how accurate is the calories burned according to the FitBit? I know it can't be spot on and just bases it on the average of a person of my height and size - what do you do?