Get one like this. Simple is better. Stay away from the ones with all the add-ons.

Amazon.com: Polar Heart Rate Monitors – FS3 – Basic Fitness – Model 560139: Health & Personal Care.

This is how to establish your own personal Heart Rate settings:

Top Working (Maximum) Heart Rate:   220 – your age   ( example: if your age is 35 yrs old;  220 minus 35 = 185;     185 is your top HR)

Recovery Heart Rate:  60% of Max HR    ( example: 60% of 185 = 105;     105 is your Recovery HR)

Using the 12 week jogging program outlined in the Post One Small Step for a Man(found below), you will need the HR monitor beinning in week 7.        Jog until you reach your Max HR, then walk until your heart rate falls to your Recovery HR, then jog again till it reaches your Max HR, then walk….like so until you’ve completed the recommended time in the program.

Using the HR monitor allows your body to override your expectations and daily flucuations in fitness. It gives direct feedback on how much you can do on any particular day. As you progress your HR will take a longer time to reach your Max HR, and shorter time to reach the recovery HR, and that basically is all there is to areobic fitness.

The most difficult part by far is just getting yourself to the track.