Walking a mile at your weight will burn around 140 calories. Assuming you’re walking 2 miles per session, every day, you’re burning about 2,000 calories per week, or enough calories to lose a pound every other week, but only if you’re already consuming as many calories as you’re burning.
Exercise is a very inefficient way to lose weight compared to diet. 300 calories per day is valuable but that’s pretty easily wiped out by one snack or poor eating decision. I’m not a trainer or a nutritionist but here’s what I’d recommend:
Figure out how many calories you need to eat per day to maintain your weight. There are calorie calculators online that will account for your height, weight, age and activity level. Use little or no exercise in the calculator.
Track every single thing you eat or drink and use this info to create a 250 calorie per day deficit. Meaning, if someone at your height or weight is supposed to consume 2,800 calories per day to maintain his or her weight, you have 2,550 or less. You should lose a pound every other week just through diet without starving yourself.
Get a cheap gym membership and start walking on a treadmill. This will help you more accurately track your distance and calories burned. I’d initially shoot for a consistent distance for example 2 miles per walk. When this becomes routine and easy, up the incline slightly on the treadmill. This is hugely efficient in burning calories.
I suggest having a regular mental health rest day and adding a endurance based weight training to your cardio. For example do the walk 4 days per week but twice per week lift instead.
Between the exercise and diet you should easily burn a pound a week or more. And it should be a lot more sustainable than starving yourself and going 150% on the diet and gym.
I guess to answer your question, walking every day is huge versus no exercise at all. But diet is 75% or more of weight loss.
Good luck.