AI technologies can be created by letting algorithms learn from data without much human supervision or coding. This process is generally known as machine learning. With machine learning, the computer is given a large amount of so-called training data, as well as an instruction to do something with it. It can then learn about the relationships between data points with some human help (e.g., by humans already labeling some data), or, as is common with the technology behind LLMs, mostly on its own. Through parallel processing, machine learning can process large amounts of data very quickly. The resulting AI technologies can be very efficient and powerful, but given the limited involvement of humans it can also be very difficult to explain how these technologies get to their outcomes.
In the case of LLMs where the instruction would be to generate a humanlike text, the computer learns patterns in the training data by itself by processing a large corpus of language data. It then uses those patterns to achieve the desired.
'Large amounts of information being transferred to a machine', Microsoft Designer