traing using HRM

[konati]

Trying to get a handle on the different training zones. If I understand it correctly to train in the endurance zone the heart rate should be 70-75% of your max, is that correct.
Why I ask is to me that seem way to easy so do I have it wrong? All of my training is done on a bike so at 75% of my max I could ride all day but certainly not fast. So do I devote a few day a week to that and include intervals? The days that I am riding a lot of miles should Perpepuim be my main source of calories and would I include heed in another bottle or combine them in the bottle.