People get mad when you call LLMs "spicy autocomplete" but my investigations into recreating and implementing small versions of this tech make me think that nick name is very accurate.
Basically, it's a method to predict the next content in a text file. The whole conversation between you and the LLM is one file, and the LLM tries to find the most likely next text based on the training data.
There is something significant here: LLMs were trained on internet forums and social media.