So I was just thinking about that stuff and I think I've realized the purpose of the functions.
Ni and Si are the inward understanding functions. These allow you to gain inner realization and understanding about things in your life based on mental processes, whether it through intuition or things around you.
Ne and Se are the outward understanding functions. These allow you to gain understanding of things in your life through either the things you see around you or the things that could be around you. (over generalization)
Te and Fe are the outward application functions. You apply things to the real world from within with these functions, whether it be logic and order or another's needs.
Ti and Fi are the inward analyzation functions. You analyze things going on in your life through these, whether it be with logic and facts that you know, or whether it be with emotions and how you feel.
So as an INFP (FiNeSiTe) I analyze the experiences in my head, then apply what could be afterwards from that. Then from that I realize the details of things from my inner analyzation, then from all of those being used I can apply it to situations in my life.
This is just a simpler explanation as to what they are for (or what I think they are for). Thoughts?