Weight loss is based on building a calorie deficit. You need a deficit of 3500 calories to burn off one pound of fat.
Personally, I’d choose exercise any day over dieting. The recommended calorie intake for a woman is 2000 a day, (it’s 2500 for men).
If you have a lot of weight to lose, you’ll lose more than one pound per week when you first start walking for weight loss.
This will depend on your goals. Just lacing up some trainers and heading out the door is going to improve your health and fitness.