We do not really learn to be one or the other, but most people are just dominant with one hand or the other and not usually both. And while we use both hands everyday, when we need to feel secure we tend to use our preferred hand. This is the same with each of the four dimensions. We use them both, but we usually choose our dominant preference when we need to feel comfortable. Introversion and extroversion are ways of orienting ourselves to ideas and people.
Extroverts work more outside in and introverts work more inside out.
Sensates see ideas more as part of physical reality and connected to what is. Intuitives see ideas as a world in and of themselves and see ideas as just as real as things. This area has much to do with preferences in communication, where Sensates often prefer to talk about what is, and Intuitives more often talk about what is perceived and interpreted. The dimension of Thinking and Feeling deals with one's orientation to making decisions. Thinkers tend to make decisions based on logic and ideas whereas Feelers tend to make decisions more based on relation to people and how their actions affect others, especially their feelings.