NLP arises in the early 1970s in Santa Cruz, California. Actually, they invented nothing new. What John Grinder and Richard Bandler achieved is to codify the patterns that brought great therapists of the time to excellence: Fritz Perls, Virginia Satir and Milton Erickson. Basically, their work consisted of modeling one of them, replicating what they had unconsciously assimilated to validate that they had the same results with people and then codified those patterns so that others could replicate it with the same results.

In turn, both creators mixed and drank from many other sources that fertilized their work: the writings of Gregory Bateson, Korzybski, transformational grammar … All in a university environment with some methodological freedom.
Communication
As they defined NLP in their origin, it is the  study of the structure of subjective experience.
That is, each of us lives an experience, each subject lives their experience, so it is subjective and one could not study the millions of experiences that all subjects live. However, every subjective experience has a structure and this is what NLP studies.
John and Richard realized that these 3 therapists had common structures in their communication, which unconsciously adapted according to the client and obtained brilliant results. That is why one of the fields where the greatest impact has been on NLP has been in communication.
Can you imagine how your communication would improve if you knew how your interlocutor processes the information? It would allow you to tell him things so that he could process them more easily. This helps us to be  more flexible  and to be able to relate better, with ourselves and with others.
emotional states
Understanding how we think and feel , helps us understand how is the reality that we represent ourselves internally. Does it help me to be more successful or is it holding me back? Notice how when you go to the movies with a friend, each one is left with different nuances and sequences of the whole movie. That same happens with the reality that each one lives, it is represented in a different way internally.
And it turns out that perhaps the internal representation that you have done is not being useful to you. It may be leading you to negative thoughts, not useful emotions and, consequently, the actions are disastrous. NLP allows you to identify your internal reality and if it is not useful to be able to readjust it with simple techniques, to  enhance thoughts, emotions and actions  that lead to better results. Something that perhaps in certain situations we do unconsciously, in others, because of the emotional load, we may not know how to do it consciously. With NLP you train to have a tool kit to use at any time.