1800 calories diet

I've been dieting since two months but now i feel def deprived and i'd like to have got a healthy diet because of time my net calories were under 900 since i exercise quite a lot (3-5 times a week). My questions are : 1. If i ate 1800 calories and i burned 400/500 would i lose weight (FAT,WOULD I LOSE FAT?) 2. Never understood this: if i eat 1000 calories till miday( breakfast,snack and lunch) and then i exercise a burn 400 calories would it mean that basically i've eaten just 600 calories so if my diet is 1800 calories i need to eat other 1200 calories or it's not good for losing ?