Any regular increase in energy expenditure with calorie intake remaining the same will cause some weight loss. Neither walking 5 miles, nor jogging 3 miles will make a huge difference, but it will make some difference.
Happ000 For most people the basic rules apply. 1lb of fat=3500 calories. Want to loose a lb a week? Then you need to consume/eat 3500 calories less than you burn. 2lbs a week 7000cals. There is a great, free app available on iOS and Android called Loseit that basically does all the work for you. At work I can end up burning as much as 300 cals walking or as little as 50 so I use a pedometer app too. Loseit wil help you track your foods and activiy levels. It is important to match these as you do not want to send your body into starvation mode. To avoid this, the generally accepted max weight loss is 2lb/week.
Rather than going on a crazy diet and or walking for 90mins a day every day in the week (or whatever), my advise would be to use an app like loseit as a tool to make sustainable, long-term changes to your diet and activity levels as well as becoming back in tune with how much your body actually needs to eat. That's what worked for me anyway. 60lbs down. Dont fret too much about stuff being low fat at first, just monitor the calories in and out.
In any case, walking is a great idea. It will help with your mental health, base cardio ability, boost your metabolisim some and therefore likely help with your energy levels too. All great things. I would stress again though, choose a time/distance and frequency that is going to be sustainable and enjoyable for you.