My advice is that controlling one's diet trumps any level of physical exercise you can do, unless you are already physically fit. That is to say, for inactive to moderately active individuals, one's diet has much more influence on health than how much one exercises.
Of course, this is not a rationale to avoid exercise. Quite the contrary: it is essential to be physically active. But in my experience, one of the most common pitfalls that people make when first starting out is that they go gangbusters on the exercise without scrutinizing their dietary/lifestyle habits. Then they suffer pain or injury, and they end up gaining more weight because of reduced mobility.
Initially, I would limit physical activity to walking. Whether on flat pavement, up hills, or up stairs, it's all good. Walking at a brisk pace for a sustained amount of time (60-90 minutes per day) is an excellent, safe way to improve cardiovascular health for beginners. It is easy to increase the difficulty level, and it increases muscular and skeletal strength in preparation for higher impact activities. But you have to be consistent to see results.
Your extra body weight, at this stage, is actually working in your favor. People who are already athletic often fail to realize that overweight people are constantly bearing that extra weight, which automatically increases the difficulty level. You don't see runners going for their 5k or 10k jog with 150 pounds of weight hoisted onto their shoulders, do you? Even an extra 50 pounds makes a huge difference.
But back to what really matters: diet. The biggest thing you can do is eliminate refined sugars. Nothing with high fructose corn syrup, or sucrose/cane sugar. Eat more fiber. You don't need to cut out fat or meat or complex carbohydrates, but do avoid things like soda (diet or otherwise) and fruit juice. Count your calories. If you ran 5 miles in 1 hour, you would maybe burn 600-900 calories. You could eat 2-3x that amount in a single meal, let alone drink that amount in soda. So you can see that exercise at this point is not going to be the primary controlling factor for weight loss.