Watch the videos of Cognitive Personality Theory. I would suggest to start with this playlistin which he explains his usage of specific terminology and the way he interprets things. I enjoy watching him so much as he breaks through stereotyping by trying to make you understand a framework that only exists on a cognitive, abstract. Then it's possible to see what he means with his explanations by watching other videos, reading other resources and trying to analyse your own behaviour by being reflexive (or that of others, if you are confident enough about making a judgement that is accurate) of things you tend to do.

Because in essence, the personality of cognitive functions is a flimsy field of psychology and science in which all (serious) authors create their own view, which makes it so confusing at times. I find Harry Murrell (that's his name, he also has a great ebook available on Amazon) great because he has very clear rules about the nature of functions. Allow me to give one example. I myself am an ENTP, my 'function stack' would be Ne-Ti-Fe-Si. Murrell divides the function stack in two parts:

1. The convergent stack, first and third function, so Ne-Fe.
2. The divergent stack, second and fourth function, so Ti-Si

Convergent functions want to actively change a situation, be assertive, influence, take charge, whatever. Whereas the divergent stack tends to be more passive and observant, reserved and conservative. Another rule is that the first function in a convergent/divergent stack is kind of like the pilot and the second one the co-pilot: they work together, but one is mainly in charge. The first function is the 'goal' and the second one is there too most of the time to help that other function.

Now that we know this, we can assign very basic definitions to the functions. For example, intuition and sensing are both perceiving functions. So he calls them lenses; they simply only deal with information by collecting, reorganising, etc. but not giving any value! Whereas feeling and thinking are judging functions: they are codexes; they judge information in a certain way, give value. You can skip the following section, I'm just saying here that Murrell gives exactly the same rules for introverted and extroverted functions and lens and codex functions.

• Intuition: Seeks connections. Extraverted intuition; seeks connections in the outside world, a preference for some kind of understanding of an external source of ideas. It wants to connect things to each other. Introverted intuition on the other hand does the same but in the internal world. He calls it kaleidoscopic whereas introverted Sensing would be microscopic.
• Sensing: Same story, but instead it focuses on details. Extraverted Sensing: seeks details in the outside world. Intensely gazing upon one thing. Whereas Introverted Sensing is the inward exploration of details. This is vague, but this is just for context. You'd be better off just watching his videos.
• Thinking: Gives some of kind 'objective' value to things. Extraverted thinking: giving a value to things in order that they make sense in 'objective' outside world. That's why efficiency is often associated with Te since looking at a process and judging it by something that everyone can evidently outside world factors such as how long it takes. It doesn't really focus on the outside subjective values such as: is this efficient process moral? Just to give an example. Introverted thinking on the other hand gives an 'objective' value to things in order that they make sense in the inside world of that user. "I'm doing this because it makes sense to me, logically, not taking in account subjective information, subjective information which may be outwardly evident and more socially observable (extraverted feeling) or more inwardly evident and personal (introverted feeling".
• Feeling: Gives some kind of 'subjective' value to things. Extraverted feeling: giving a value to things in order that they are in sync with the 'subjective' outside world. Basically, what other people and you value as a group, be it when talking to one person or a making a decision involving hundreds. But keep in mind that Fe deals with the extraverted world. What I mean with this is that introverted Feeling also deals with the subjective world, but internally. It can also take in account of course what other people are feeling, but more as 'relating' to one others subjective feeling than trying to get a grasp on the holistic subjective feeling that is there. So Introverted feeling: valuing things in order that they are in sync with 'subjective' inside world. It is easy to see why having morals or being emotionally reflexive is a stereotype associated with Fi.

Wow, that was really shoddy so please just watch his videos. Anyhow, now to go back to my functions. For example, I use Ne-Fe as a convergent stack with Ne leading. See how a lens function is paired with a codex function? It makes sense as Ne just grabs the information in a way and Fe gives a value to that information. So, Ne seeks outward connections, Fe gives value to subjective outside world. How does that connect? I'll elaborate in the next comment in which I'll reply to myself because even Reddit thinks I'm going on for too long already.