These notebooks are created by taking sections under the headings in the starter kit such as Setup AIcrowd Utilities, Training Phase, Prediction phase.
You need to put code in the starter-kit under the respective sections and then create these notebooks using the %aicrowd notebook submit command.
It will be ideal to add the code directly into the notebook but yeah you can still addpy files in the zip directory.
I ran the starter kit getting-started-notebook-for-language-classification.ipynb. It created submission.zip which contained 4 aforementioned notebooks, but install.ipynb is empty, the content of train.ipynb and predict.ipynb is the same as original_notebook.ipynb.