In a nutshell:
Extraversion vs. Introversion (E vs. I) describes how a person gets energized
Sensing vs. Intuition (S vs. N) describes how a person takes in information
Thinking vs. Feeling (T vs. F) describes the means a person uses to make decisions
Judging vs. Perceiving (J vs. P) describes the speed with which a person makes decisions
Some tests that purport to measure Myers-Briggs indicators are less accurate or less detailed than others but the indicators themselves are neutral, they just show where you fall on a sliding scale for each category. For instance, someone could be 20% introvert and 80% extrovert, it just means they are more extroverted than someone who might measure 40/60 or 80/20.
There are several free tests online, most folks who take them recognize themselves in the descriptions of the results although a lot of the more casual descriptions are too broad and don't take in the nuances of four sliding scales interacting.
