Trying to run a kaggle notebook
The actual code is included in the notebook, if you click on the 'Code' button just above the cell with the code you provide you will see the code used to define the train_model function. If you look in that function you will see that this function can use different models based on the model_type argument, and in the line of code you linked 'lgb' means that a gradient boosting model from the lgb library is used.