Happy birthday NZC and aren't you a lucky girl, that is the top end, very latest, posh version.
I have the 405 with HR and footpod, it is similar to yours without the fancy touch screen and it also has a number of bugs that yours doesn't.
Very happy to help you get into getting the most out of HR monitoring.
First and foremost I should say I am not a big advocate of running by HR much more post run analysis to see where you are and assess what you need to be doing. Once you have been using it for a while you will find that your subjective feel becomes quite accurate and as long as you continue to use your HRM you stay calibrated.
Runners have a very wide range of HRs, some have high rates some have low. It does not seem to be related to your fitness but more to your genetics and physical size. I have a max of 187 but ceal and TS are in the 160 range
To intepret your HR absolute readings you need to establish your HR range, that is your max and resting values.
Your resting HR is easy to establish, just take your HR while still lying in bed first thing in the morning. I would suggest doing it a few times as it does vary a bit.
Your max is a little tougher to establish. All the formulae that you see are very very unreliable and should be avoided.
You can do a Max HR test but I have not found them that reliable or easy to do.
I have found my max from 5k racing. An all out effort 5k will take you close that is within 4 or 5 bpm.
Having done this you will now have your working heart range, that is Max - Resting, for example mine is 187 - 45 = 142 bpm.
At this point you can compare your HR numbers with normalised heart rate zones
For example if you are running at 70% of your working heart range (WHR) that is considered an easy or recovery run. It is usual to express your HR as a % of your WHR.
For example if I was running at an average HR of 150 bpm then I would express that as 73.9% WHR
( 150 - Resting) / (187 - 45) * 100 = 105 / 142 * 100 = 73.9%
Your Lactate Threshold, that is where your body is producing as much lactate as it can process without it accumulating excessively in your blood, is usually in the low 80% range. This is an important number as it reflects the effort level that is typically the pace that you should be able to run a half marathon at and also the effort level that you should be doing your tempo runs at. I find this one of the most useful levels to establish and calibrate yourself at.
I would suggest you run with your HRM for a while and just collect some data. Run an easy run and look at the HR profile, it should be flat after an initial ramp up and be under 70% WHR.
If you can produce screen shots of the HR profiles I will be happy to comment on them.
I have written all sorts of software to enable you to compare runs and post your results so if you are comfortable installing software I can help you with that.
Hope all that is not confusing.
Mick