THE COGNITIVE FUNCTIONS, DEMYSTIFIED
Ni -- Introverted Intuition (not Nickel, which I know is what you thought). Allows you to see ideas from different perspectives, as well as have unusual insights or hunches that are often useful. And for the last time, it does NOT make you psychic (normally).
Ne -- Extraverted Intuition. It thinks it's less of a nerd than Introverted Intuition. Kidding aside, this allows you to see patterns and connections in theories, see several possibilities in a situation, and make an annoying number of puns and play-on words.
Fe -- Extraverted Feeling. Hello everyone, this is the function that observes commonly held social rules and pleasantries, and is very concerned with the welfare of the group. If you don't have this function, then you're a rude person, and I don't want to be seen with you.
Fi -- Introverted Feeling. Very shy, deeply held values based on an internal sense of good and evil. Introverted Feelers are often lost in the depth of their own emotion, and have trouble expressing those emotions outwardly. If you've read Shakespeare or Milton, you may have seen Fi. (Notice I didn't joke about them, because they're SO sensitive.)
Ti -- Introverted Thinking. Introverted thinking is always trying to uncover the specific rules that govern a system, and typically sees everything as a system. So basically, Ti nitpicks and criticizes everything from social conventions to grammar to government policies, and is fairly anti-social.
Te -- Extraverted Thinking. "Hey, work faster, you slacker! You're losing us time and money!" Extraverted Thinking is a blunt function that is results-oriented, much like that angry boss. Extraverted Thinking follows rules to the letter, and uses the most efficient procedure known to work that will get the job done.
Se -- Extraverted Sensing. This is basically paying attention to what goes on around you, and living the moment. You use this if you like to burn yourself on a hot stove, run laps, ride a bike, go swimming, etc. If you want to use it right now, pay attention to what's going on around you at the moment. Don't try to connect it with anything, or think about what it means, what went before, or what's coming after. Just watch and experience. Let go of your mind. Side effects may include lack of forethought, and overindulgence. This is also what causes you to eat that box of chocolates instead of sticking to your diet, or finish watching that TV program instead of shutting it off and going back to work/bed. Now you can just say, "That was Se's fault, not mine!"
Si -- Introverted Sensing. Very routine, habitual, and boring. It's based on a desire to do things the way they've always been done... day after day, year after year, century after century. Obviously, people with this function dislike change. They accept things without question, and preserve what's familiar, and often try to align things with their internal idea of what things are supposed to be like, garnered from early experiences. But the plus side is, they have good memories, and are very organized and conscientious people. If you want something done a certain way with no questions asked, they are your best resource.