Well you could jog in place, or do jumping jacks for calisthenics, basically anything to get your heart pumping. If you want to strengthen your legs you can do squats, which basically just means stand with your legs shoulder-width apart, then squat down until your thighs are parallel to the ground, with your calves still at a 90 degree angle. Do like 100 of these and you'll definitely feel the burn. Also you mention walking, but you should get a good bike and ride around instead. Not only will you get to go more places, but it's better on your knees and also you're more likely to get a good workout out of it.

The key is to not stop though. Push yourself just a little bit past what you think you can do, but keep at it for at least an hour at a time, at least three times a week.

I'm curious, what makes you say you can't do push ups?

I agree with Lazlo. Try simple exercises like jogging, jumping rope, jumping jacks, bike riding, squats.

If you want to improve muscle definition then you can look up workout tutorials online. There are some really useful videos out there showing techniques for weight-training using the weight of your own body (example: push-ups).

If you can't do an exercise, then you just need to build your endurance. Do it a few times until you are tired. If you keep doing it a few times every time you work out, eventually your muscles will strengthen and you'll be able to do it easily.

Also, stay hydrated, drink a ton of water (as much as you can) before, after and during exercise. And eat a good nourishing meal after intense workouts or your body won't have fuel to recover.

Oh yeah, I forgot to mention, stretch after an exercise! When you exercise, you tear the muscles you're using, and when they rebuild that's what makes you sore (sort of) but it's also what lets them get bigger and stronger, and to mend faster and better, they need blood. Stretching allows your blood to access these areas of your body more easily.

Running. Simply running boosts most of your needed muscles.

And hell, doing anything that moves your legs is generally good exercise.

Well in my opinion, I think push-ups and sit-ups are good workouts too.

I think it really depends on the person and what their body is able to handle. But I can give some ideas and suggestions. Cardio is the best I have found to get a good workout. Can be high or low impact, doesn't really matter. Just whatever level you can handle. Waling is probably the easiest form of exercise and really effective. You can even start out with walking and work your way up to jogging and then running. Again, just see what your body can handle. I never go by what others can do, I only go by what I can do personally. Some things I can do and other things I can't do. Like legacyme3: is a runner, well if I did that I'd probably collapse and end up with a heart attack. Haha. But I can speed walk, that's as high as I can go with that kind of exercise. Another good form of exercise is bicycles. I don't consider that equipment, I think of it as a recreational activity that can give you exercise, that is a bonus. Or jump rope, yeah sounds childish but it can help as well.

It also varies on what you enjoy doing. Some people may love to do some of the things I listen while others prefer other forms of exercise. Some people are into sports, like basketball. I used to play when I was in High School but i wouldn't be able to do it now. Or they enjoy extreme sports. All depends on what you will enjoy doing and what your body can handle. I wouldn't want to do something I hated or made me black-out. I hope I gave you some good ideas/suggestions.

The best work out i do is to first lift a little bit of weights after that i would run up and down the block 5 times, then i would go inside and do sit ups.