If you are just starting out as a runner (or a walker) I thought I would give you a couple of ideas of different training programs that I have used (or am using now!)
I use the Nike+ app to track all my runs. It breaks down my pace, overall time I've been running, mileage & calories burned. You enter your personal data (age, weight, height) and it is pretty accurate. It also keeps a running tally of miles completed and I love to watch the number grow :) Right now I'm at 789 miles (thats over the course of about a year and a half) and can't wait to break 1000! You can also go back in and see your "record breaking" runs- fastest mile, fastest 5k, fastest 10k, fastest half marathon, longest run, farthest run) Its definitely worth the 1.99 and I use it every single day.
If you are a VERY beginning runner (meaning you DON'T run at all, or can run 1-2 minutes at the most) then I suggest Couch 2 5k. There are several different .99-1.99 apps available for the iphone (and I believe Droid and Blackberry also) Its a 9 week program that takes you from NO running experience to being able to successfully run 30 minutes at a time. Its really well designed and the intervals are challenging, but not impossible. If I never would have done Couch 2 5k, I probably wouldn't be as committed to running or love it as much as I do now. It's great! (I'm actually re-doing the program right now, but working on my speed instead of endurance. I'll start my half training as soon as I'm done with this)
Once you are done and comfortable running a 5k (3.1 miles) you can move on to Bridge to 10k. It is designed for runners who are increasing their distance from a 5k to a 10k (6.2 miles). This would also be a good one to start with if you are already comfortable running a couple of miles at a time. I definitely wouldn't start out with this one if you aren't a runner already though.
And my all time favorite for half marathon training is Hal Higdon's program. There are several different levels (Novice, Intermediate, Advanced, etc). I used to to train for my half in November, followed it to a T (besides adding 2 "long runs" to the end of the program) and I felt completely compared to run 13.1 miles come race day. It was hard & I was scared, but I knew I was capable of doing it. I'm definitely looking forward to starting my training again for the race in May. Hal also has a full marathon training program that I'll do when I'm ready (next year?)
If you do not have a smart phone, all you need is a simple stop watch to time your intervals (mostly for Couch 2 5k and Bridge to 10k)
Also, if you don't use a GPS device (Garmin, phone app, etc) then you can go to www.mapmyrun.com
and track your route, so that you can determine how far you ran.
If you don't like running outside, you can always hop on a treadmill! In that case, you don't have to worry about a device to track your pace, time or distance because the treadmill will do it all for you. Personally, I avoid the treadmill :) It's not my favorite, I definitely enjoy running outside, getting fresh air and not being stuck in the same spot for 1 hour. But- everyone is different!
So- get your running shoes & some comfortable clothes on and get ready to hit the pavement (or the treadmill). You CAN do it! No matter what fitness level you are starting out at, you ARE capable. Just keep reminding yourself that you are worth it and you deserve to feel and look the best you can!