How often and how intense should a work out be when first starting out?

Gradual: What you want to avoid is the "weekend athlete" phenomena where someone in poor condition exercises much more than they are used to resulting in an injury. If you have not exercised much, you want to start gradual. One way to do this is to monitor your heart rate and shoot for usually about 80!percent max rate for aerobic benefit. Check with your doctor before starting an exercise program.