I don't think I can really do that in a nutshell.
I've spent years trying to figure out how to explain it to other people. I actually joined HN in hopes of learning to program so I could write a simulation to more effectively convey the information, but that hasn't happened. Getting well and other life drama has taken all my time.
Trying to explain it with mere words seems to be something that needs like a million of them and still isn't really adequate.
But, in a nutshell (or an attempt at a nutshell explanation):
First, I did things I knew were helpful from before having a diagnosis and tried to then go figure out why it was helpful. Having gotten diagnosed late in life, I had my own mental models and ideas that didn't jibe with our current official understanding of the condition. I respected my innate knowledge rather than just agreeing with the experts.
Second, I tried to understand the pathology. We know the mechanism behind the condition: A malfunctioning (or sometimes missing) cell channel called the CFTR that handles trafficking of certain molecules into and out of the cell. So I tried to understand how we get from there to all the symptoms typically associated with CF, such as malabsorption and lung infections. That seems to be a different approach from what medicine currently does.
Some of my general conclusions:
Malabsorption leads to malnourishment. Many of my issues were rooted in malnourishment. Improving my nutritional status was a major cornerstone of my efforts to get healthier.
I found ways to compensate for the defective cell channel. One thing that is known is that CF involves misprocessing of fats. I got very picky about what fats I eat and tried to develop some understanding of why some fats are helpful and others are problematic. This seems to be rooted in chemistry and at least partly in how complex the molecule is. My body generally handles long chain triglycerides poorly and I favor medium chain triglcerides, though that is likely a wholly inadequate explanation of the phenomenon.
Most genetic disorders involve a misfolded protein. I learned what promotes misfolds. Chemical derangement in the cell promotes misfolds. I believe this is an important mechanism behind the progression of CF, where you steadily get worse. I think reversing the chemical derangement stopped the positive feedback loop (aka vicious cycle) and this was a huge, huge factor in being able to get healthier rather than just try to slow or halt the progression.
I'm currently trying to figure out what I want to say on my blog about my understanding of "the immune system." When we speak most systems, we can name specific organs. The digestive system involves the stomach, small intestine and large intestine. The circulatory system involves the heart and an extensive system of blood vessels. But I can't list for you the organs involved in the immune system.
So I think better understanding exactly what we mean by that -- what is going on when the body successfully fights off infection -- is a major thing and I am still trying to figure out what I want to say about that. I think we generally have a poor concept for how that happens.
That's probably several hundred thousand words short of conveying much of anything, but it's an attempt to reply to your question.