Reddit mentions of Marathon: You Can Do It!

I recommend the Galloway Method and this book to everyone. I've been doing run/walk for virtually my entire ten years of running. I use the app RunMeter because the premium version (for a whopping $5/year) allows you set run/walk intervals. I listen to podcasts for most of my runs, and fortunately we've got great trails for running where I live. You can also check out Jeff Galloway's website, and several of his training plans are on there for free. It's quite possible your library will have his book as well.

I do have to say, the less you weigh the faster your times will be. It's the simple physics of it takes more energy to move more mass. But more than anything, be consistent. Work up your distances slowly, but be consistent.