Start walking. The trick to healthy walking is not doing it today. The real trick is doing it tomorrow and the next day. We aren't talking about a stroll around the mall. Get out there and stride!
My first walk was 10 minutes around the block. I was exhausted. I could have quit but I went out "tomorrow," and the next day. Then I ran. A 5k, 10k, duathlon, triathlon, half marathon. Now training for a marathon and my max distance is 18.46 miles.