Basic Principles Behind Change in Eating

I joined today and have played around for a few hours now with the menu planner. I’ve wandered around through the pages, perused some of the articles, and maybe I’m just too eager or maybe I’m just one of those people who is a “need to know” type, but beyond the balancing system in the menu planner, I don’t see a link or article that explains HOW to balance food – meaning, how do you know how many carbs you need with your protien for snack #2, and why do you need a sweet? There is obviously some train of thought behind all of this, and I guess, I want to know more. I have a busy lifestyle, and I’m not sure that I have hours upon hours to play with the menu planner to figure out what to eat and reality is, I’m out of town quite frequently and I don’t want to have to pull out my PC before a business dinner say, “wait a minute, I have to plug this into my meal planner to see what I can eat…”

Can anyone direct me to a link that explains how I know when and how to balance the foods?