Lately, I take a walk for about a mile every day.
I do software development. Except when I'm meeting with clients, it's mostly a sit-down job.
I'm about 20 pounds overweight. On a 5'10" frame @ 190#. I don't look fat, but technically I'm overweight, and I can see it. Somebody seriously overwieght would love to have my numbers.
Mostly for me, I reduce my intake. Cut down on the crap-food. it helps. I used to have a very fast metabolism. I could eat a frozen pizza every night in college for dinner and still be underweight.
there's some studies out there that indicate that the key to weight loss is diet, not exercise. Not that exercise doesn't have benefits (like staying fit, which is not the same as being in your ideal weight range). Given that once an over-weight person is down to healthy size, they still have to manage their diet, regardless of anything else, it's a basic mathematical truth.
What exercise will do for you is improve the muscles you have (like heart) and increase caloric burn which will help lose weight faster. Also pretty obvious.
My point being though, you can start getting healthy by cutting back the crap food, especially excessive amounts. Ordering more than 2 of anything at a restuarant (like 3 hamburgers or 6 tacos) is too much food, regardless of its unhealthiness. the stereotypical problem eaters can often be seen ordering large orders. That alone is bad for anybody.
Now my wife, has spent over a year getting in shape. She was about 180# on a 5' frame, and luckily didn't look "fat" but was more overweight than me. Thats still a lot of weight on a small person, but she didn't look "obese". She's beeen hittting the gym, running at home, etc, and she's lost 30 pounds. So she's looking pretty fit right now, though for her height, she can still lose more weight. For her, the main factors are doing classes that are meant to be hard work ala "biggest loser" at the gym, and eating way more healthily. She avoids white bread , rice or pasta, eats lots of veggies, avoids fast food and pop. She counts her calories and stays under budget every day.