The three centers I refer to are the Head, the Heart, and the Belly. In some sense they are like three little worlds, but since all are in one body, they are part of a larger whole.
The Head center is the world of concepts, perceptions, and principles. It is the world of the scientist and the engineer, the philosopher, and the religiously subtle. You think about problems, mull them over for a while, and come up with symbolic solutions that make sense to you. If you are a scientist, then the solutions must be correct, they must make sense to all other scientists. If you are a philosopher or religious thinker, your solution ideas must make sense to others in your group or sect.
The Heart center is the world of feelings and inklings both subtle and obvious, both painful and pleasant. Of course, there are many neutral feelings and sentiments, but the strong positive and negative ones are the ones we remember best and influence us the most. Some people return to their heartfelt feelings about a situation when they need guideance or to make a decision, and really rely on their intuition and sense of fairness and how they feel as a reference guidepost.
The Body center is the world of movement, health and wellness, physical strength, and stamina. The physical body supports the worlds above it, but you can be employed to do physical tasks or teach others to do physical tasks, and for this you need to stay healthy. Western medicine is mostly concerned with the mechanics of staying well or mechanically removing disease; Eastern medicine integrates the Heart center and the Head center in the process of being physically healthy.