Figuring out your type is easy, you just have to know yourself. Not who you want to be, but who you are.
I vs E, which one are you? It is quite easy as how much time do you spend alone, and do you feel more energized by others or by being alone?
N vs S ... read the definition of both, and you are definitely one or the other. Worst case is you have them both equally developed, but even then you should prefer to use one. If you have N developed it is likely that's your preference, sensing is only useful for practical stuff, N is more interesting and intriguing. People who use S all the time only do so because they lack N.
T vs F ... Would you reach a decision and follow through with it, even if your emotions did not agree? Or can you even feel your emotions? If you often feel emotionless, then you are T. If you think analytical types are too heartless and prefer to make decisions to bring about inner peace and resolving of conflict, then you are F.
J vs P ... Look at several things for this... How clean is your living space? J's tend to be better about cleaning, but cleaning also requires some level of sensing for one to be bothered by a mess. After all, if your brain never registers a mess, then your judging doesn't pick up on the mess and decide to organize it.
Do you sometimes hear some idiot talking and think in your head how wrong they are, but decide that them being wrong is just your perspective, and that they have their own perspective? That's very P. When I transitioned from J to P, internally I had a realization that everything is relative. I may have formed some absolute in my head, but if another person believes the world is flat, then for that person the world is flat and that is their truth.
P = Observer, Passerby, Non-Judgmental
J = Judgmental, Acts upon Judgments
That's pretty much it, you can get some of your functions more developed and some less developed, but essentially you have a preference for each and that determines it all.