When I first started working out, I tried the heart rate monitor on the cardio machines, but I had no idea what the numbers meant! I knew I was starting to sweat, but I never knew when I was at the right heart rate. Sure, there were charts in the gym, but my age group was not listed.
Decoding the Chart
I try to keep my heart rate at 150BPM which is smack dab in the middle of the target heart rate zone! I try not to push myself too hard during workouts because it's dangerous. I'd say aim towards 140-160 BPM as long as you don't have any pre-existing heart conditions.
How I manage my heart rate
I normally take my heart rate using the cardio machines that have the heart rate monitor option. I'll take it from time-to-time during my workout because the heart rate conductors are normally in terrible spots (like on the non-moving arms of the elliptical). I'd much rather not hinder my workout by worrying about my heart rate the entire time.
As for taking my heart rate when I'm out on runs, I have begun to gauge myself on how I feel during the run and my breathing. If I'm panting and can't catch my breath-- I'm clearly going too hard. On the other hand, if I'm feeling good and I don't feel that I'm working hard enough, I will certainly push myself harder!
One day, I would love give myself a heart rate monitor! I feel like it would be extremely beneficial to have one for outdoor runs and even on the treadmill--because it's not safe to check your heart rate while running on a treadmill!
Good luck monitoring those heart rates!