See below. A gentle home exercise program that focuses on core strengthening is going to be your best bet. A great resource for this can be found at www.therehabzone.com.
"Superman" exercises. Back pain should always be checked by your doctor, especially if chronic or if one experiences symptoms down the leg(s). The superman exercise is ideal for strengthening the back muscles. Lie on your stomach, arms outstretched in front; lift the rt. Arm/shoulder and left leg/hip off the floor for 5 seconds, then repeat on the opposite side, do 12 sets, twice a day. Also, see my health guide.
Good question. There are many exercises that focus on the lower back. Despite their differences, there has never been definitive proof that one form of exercise works better than another. Also, there is evidence that the more physically fit you are the less likely it is that you will have chronic back pain. I cannot give you specific instructions, but a specialist in this area can help you.