What's in a heart rate anyway?

So I'm officially in training! I've been taking spin classes 2-3 times a week for months, running my C25K plan for the last 4 weeks and for the last four days doing Jillian Michael's The Shred. I feel good. I feel tired. But that's all good. The Shred is hard. Shouldn't be that hard but I've noticed a difference all ready, so I'll stick with it, till I can't walk anymore.

So this is going to be a short post because I would like to hear from you. What's in heart rate anyway? Bascially I want to know at what heart rate / level (I don't even know what I mean here) I need to work out at to train my body to ride for 100 miles in June and to be able to run comfortably again.

I have some very dedicated (and talented - don't tell them I said that - smile here) athletes in my family and honestly, they're a bit intimidating when it comes to this stuff. They live and breathe it. They don't have kids and aren't married. It's very important to them and I kind of get that. It's kind of all that they talk about. So they have the luxury of working out when they want, having coaches and fancy gear. My life is my kids and my husband and trying to keep my head above water. So while I want to complete this 100 mile bike ride in decent fashion, I also don't have a ton of "extra" time to do whatever it takes. Nor do I have an income that will afford me a new bike. Thanks to Daddy-O for suggesting we get me an early birthday gift. The time I will take for training will be my "Mommy time" for the next few months.

I need some good references or do I? Do I just do what I do and see what happens? Or should I "heart rate train?" How do I that?

When I run my heart rate soars between 85% - 97%. I see that and wonder if I'm near passing out or not? Sometimes it feels like it! When I ride (spin bike) I can hold on to a 75% heart rate for an extended time. I can work hard and shoot it up to 92% and bring it down within 2 minutes. I think that is all good.

Really what does it all mean? Anyone? Help...