Mary's room is a philosophical thought experiment intended to prove the existence of "non-physical" knowledge. That's a crock of shit, of course, but the solution is interesting.
Quoting wikipedia: The setup is thus: "Mary is a scientist who knows everything there is to know about the science of color, but has never experienced color. The question that Jackson raises is: once she experiences color, does she learn anything new?"
The answer is "yes". Of course she does. She doesn't learn about color - she learns about how color is represented in her mind. She learns to correlate her own "input ports" with the colors they sense.
The word "qualia" sometimes gets mixed up with non-physical nonsense, but it is a perfectly good word to describe this phenomena. If we just want to use a simple model, then the qualia of red is the "input port" it came in on - like "Oh! That's what those nerves do! They tell me "red"!".
The qualia for color correspond fairly directly with the outside territory, but the concept can be generalized to other internal states. For example, one could set up the same Mary's room setup using "anger" instead of color. Mary knows all about it from her psych class, but everyone is so damn nice to her that she hasn't yet had that experience. Lucky Mary. (Actually, I think my labrador puppy literally does not understand aggression because she's never experienced it)
Untangle Your Qualia
We experience all sorts of interesting qualia, and to a certain extent, we're all a bit like Mary. The big issue isn't so much that we have never had certain qualia, but rather that we often don't take the time to really look at them in detail. So what if Mary had seen color one day if she didn't stop to notice it? If she never bothered to correlate her inputs with what colors she was expecting, then having seen color wouldn't help her much.
One place where this becomes interesting is when certain sets of distinct qualia come bundled up in similar ways each time. If you don't look closely, you'll never notice the difference. For example, those who have played with polyphasic sleep can sometimes tell the difference between SWS deprivation and REM deprivation. As of a couple months ago, I couldn't even begin to - I never had a chance to study them in clear isolation (and hadn't been mindful enough to study the slight differences in flavor of my tiredness). On the other hand, I can break down hungry/full into a bunch of related qualia. Calorie-deficit hunger feels distinctly different from protein hunger. Calorie-surplus "full" is distinct from no-room-in-stomach full. Part of the reason I can tell these apart is from times when I was able to experience calorie-deficit hunger simultaneously with no-room-in-stomach full and focus on the seemingly contradictory qualia happening simultaneously.
Zooming in on the intricate details of our experience can get interesting. Not only can we more finely tune what we feed our bodies, but we can watch the structure of our thoughts in action. We can notice the nature of how expectation works, and use that to our advantage. We can notice what it feels like when we accept our first hypnotic suggestion - and then next time, we can recall the qualia from that experience and skip right to "deciding" to do crazy things formerly outside our LoC. It's awesome stuff.
Building With Qualia
But.. It's hard to communicate. The problem with talking about qualia comes back to Mary's problem - I can't explain the experience of color to Mary. I can't point to the "red" nerves without making them fire, and I can't do that without showing her something red.
However, it is pretty damn useful to focus on qualia when the past experiences are there. When I talk to you, I can convey the experience of looking at a red apple. You've been there. Done that. All I have to do is reference your memory of what the experience was like last time you saw a red apple. Or perhaps you have only seen green apples - I can build that experience from components of other experiences that you have had. Picture a green apple. Now imagine that instead of green, it's red.
This is what hypnotists do. If I'm trying to get you to forget your name, I'm trying to give you an experience. If you can't find the experience my words refer to, then you certainly can't have it. If you can, then we can build it from there.
And of course, this all translates to useful cases. If you want to quit smoking, the semantic knowledge that "cigarettes are unhealthy" alone does you no good. It's like knowing that red is light with wavelength from 700-635nm. What's that mean in terms of experience? Once you can connect it to the qualia of struggling to breathe when you play sports - or the future pain that comes with lung cancer - or the feeling of disappointment when you realize that you aren't the kind of person you want to be... then you can do something with it. If you don't have that, you haven't had any experience conditioning against smoking, and you'll feel that damn "I want a cig!" craving qualia.
If you want to learn to be less angry at someone, it's blocking a solution to say "I know" when someone tells you why you shouldn't. Instead, look for the experience that is suggested by the words. If you're trying self work, don't let yourself say your affirmations or your acknowledgement routine as if they're merely spells to incant - for if you do, you will make it nowhere.
The purpose of words is to connect with felt experiences. Keep them close.