I've actually dived into the theory behind these types and learned about our cognitive functions - for fun! It's hardly real science, but it does explain things better than astrology ahhah
Basically we have 8 functions that determine how we gather information and make decisions.
Ne, Ni, Fe, Fi, Te, Ti, Se and Si
The scales with "introvert vs extrovert" and "judging vs perceiving" etc are simplified dichtomies used for online tests to give a hint of what your type could be. Hence this test saying several types are possible.
I'm ENFP. That means my main 4 functions in order are:
Ne Fi Te Si
Extroverted intuition (Ne) means I gather information through a "gut feel" all the time, I sense connections and implications and live in a lot of possible futures. I also have a very easy time jumping from idea to idea, which often confuses people with low Ne lol.
Introverted Feeling (Fi) as auxiliary means I use my inner compass of morals and values to decide which ones of all ideas generated by Ne are worth following.
Tertiary Extroverted Thinking (Te) means I value taking action and being able to make good decisions, but I'm not awesome at it at all time. It helps putting my NeFi into motion at least.
Inferior Introverted Sensing (Si) means I was a messy teenager lol but nowadays I've started to think more about consequences.
For contrast, an INTP for example!
Ti Ne Si Fe
Introverted Thinking (Ti) as dominant function means you always see things in ways of logic (ish) or automatically try to fit everything you experience into a mental framework together with everything else. Everything should make sense, and you will figure out how.
Ne as auxiliary lets you spin out from Ti and be good at discovering new paths forward from what your Ti has determined makes sense. INTPs stereotypically have very active minds!
Si as tertiary can make you prone to nostalgia and value taking past experiences as a guide, but you might be pretty bad at it until you become older.
Inferior Extraverted Feeling (Fe) is why INTPs are stereotypically antisocial nerds ahah; until (typically) your late twenties or so, you're unlikely to be comfortable with expressing or being on the receiving end of emotions and might try to avoid people for that reason. Of course, we're all different and some INTPs probably learn to grasp their Fe earlier and can instead use it as a tool to understand what people around you mean and want and how you can act in order to get what you want from them.
/tl;dr it's complicated astrology but sadly without pretty star pictures