I'm going to turn this over to my wife, Debbie - she has 20+ years experience as an Aerobics Instructor:
I get the feeling you don't belong to a gym, which is fine. If you do, you can take an aerobics class, use a treadmill or some other aerobic equipment. If not, you can walk, run, or do some aerobics to music in the livingroom.
You really need to get the stamina built up, doing about 20 minutes of aerobics at least four times a week is what is recommended. You also need to get your heart rate up,so you want to go pretty fast. Using weights also helps build muscle mass and helps burn fat. One of the things people in general seem to do is start doing a bunch of aerobics and then lifting weights, then they are so sore after this, they stop and never want to start up again. I think it is really important to start off slow and work your way up, it is amazing how quickly the body responds to exercise.
I also believe stretching is important. I know people ignore this but it really takes away a lot of the soreness you will encounter in the beginning. Warm up your body first, doing at least a five minute aerobic warm up, then you can stretch out your arms and legs. Then you can do your aerobics, on to strength training, abdominals and stretching last.
When you are doing weights remember you want to work your big muscle groups first, starting with the back and chest. Do the weight training every other day!!!! The muscles tear a little each time you lift weights so you really need to let them rest the next day. When you are using weights, start with weights that feel a little too heavy, do three sets of 10 to 12 repetitions, one minute between reps. Lighter weights and more repetitions will give you lean muscle, heavy weights and less reps. builds bulk. When it gets easy to lift those weights go heavier. You can do upper body one day, and lower the next, you can do aerobics and work your abdominals every day. I am sure that every weight lifter has a different way to do your weight training, this is the way I learned.
I am working out right now at our apartment workout room, I have found doing my aerobcis first, then weight training, abs and cool down works out great. I usually spend about an hour working out. I try to workout everyday except Sat. and Sun.
There are a lot of websites that show how perform the exercise correctly, Prevention Magazine . com has some great how to do's.
I think anything you can do, even if you can make up a ten or fifteen minute workout everyday, and you will start seeing results!!!
I hope this helps, if you have any more questions feel free to reply.
Good luck, Debbie