This is the first dichotomy.
Many people take the extrovert/introvert to mean how friendly or outgoing somebody is. This is not true at all. Like I said before, the words all have different meaning than what we are used to. My instructor claims it is because the MBTI was introduced the eighteen-hundreds when words meant things a little different than they do now.
This dichotomy is about where you get your energy from.
An Introvert will get energy from being by himself and having some "alone time".
An Extrovert will gain energy from interacting with others.
The analogy given to us by my instructor is as follows:
An Extrovert wakes up with an empty bag. Throughout the day, with each interaction with another person, he puts a coin into his bag.
An Introvert wakes up with a full bag. As he interacts with people throughout the day, he gives a coin for each interaction.
Some Introverts can be very outgoing, it will just take them a little more energy to interact than an Extrovert. And some Extrovert can be extremely shy. But it is where they gain their energy from that makes them one or the other.
Hardly anyone is completely one or the other, so you may remember times when you went to a party and came back exhausted, though normally you would be hyped after such an event. Or you may find interactions with others becoming easier over time than you initially found it.
And that is the end of the first part.