If you have joint problems you will probably want to avoid impact sports. If you can't swim, avoid water sports. And if you can't walk, talk. In other words use common sense in deciding what you will do for exercise. Aerobic exercise consists of even paced exercise that works many parts of the body, and tends to burn energy stored as fat.
Aerobic exercise is very healthy, and ideal for people who want to lose weight.
Anaerobic exercise consists of exercise that concentrates on individual muslces. Anaerobic exercise is ideal for people who want to build muscle. If you've never exercised before, or haven't exercised in a long time, you should start with very little activity, and build up over the course of several weeks. Otherwise, you will be very sore the day following your first workout. A good rule of thumb is to exercise two to three times per week.