It is downloading a dataset (TinyStories) from huggingface[1]. Here you can drill down deeper into the structure and content of the source data.

[1] https://huggingface.co/datasets/roneneldan/TinyStories

Karpathy's nanoGPT has a full training pipeline using Shakespeare. [1]

The use case for this is learning in simple example.

[1] https://github.com/karpathy/nanoGPT