I've used the app Just Run Zero to 5k and it's something I'll always recommend. It breaks down every run into warm up/cool down, timed walks and time running. There is a trainer that will tell you when to start walking/running/turn back. Every few runs you'll be running more and walking less. Eventually it'll be straight timed runs.

I believe the rule of thumb for even starting to run is being able to walk 4 miles in about an hour. That would be about 15 minutes per mile of walking. If you can't do that then I would start with walking a lot first. Get your body used to moving a lot and build some muscle and endurance before you begin to run.