I haven't exercised in years, but I need to get in better shape. How do I start?

Walk. If you are just starting an exercise program, start with just walking 30minutes 5x/week. As you become stronger, change it to two short days of 30 minutes but faster pace, one medium day at medium speed for 45 minutes and then one long day of 60 minutes but slower paced this way you train your body to burn fat and sugar. Gentle restorative yoga or tai chi, swimming or a reclining bike are good.