Remember, always get a medical clearance before starting an exercise program!
When you start out exercising to lose weight, forget intensities, heart rates, and training zones. Just get out there and move. If you start by pushing yourself to the limit every day you may not last very long so take a long-term look at your goals. Start by just getting your body used to exercising again. Do this 4-6 times per week but make sure that it does not make you too sore (this will stop the frequency of your exercise). As your body adjusts you can start increasing the intensity.
So how often should I be training?
Start with every second day and build up to most days. If you have not exercised in along time you may want to start with a 10-15min walk. Try and build this up to 40-60min, then start putting in bursts of short (100m) jogs. If you have trouble jogging, walk up hills or stairs to increase the heart rate.
What Should I Wear?
When you are first starting an exercise program the most important piece of clothing is your shoes. If they are too small, you will get blisters. If they don't provide enough support, you will get knee, shin, or ankle injuries. Be sure to get advice from the sales assistant when buying shoes. If you are unsure try Cross-Trainers. They provide great support and will suit most foot types.
Other than that be sure to wear clothing that breathes. Cotton is ideal. You will be comfortable and cool!