[QUESTION] General idea about chapter 2 and specific questions

I understand the goal of this chapter is to predict the commercial value of some houses in California state. This prediction is performed using information from different districts (number of rooms, bedrooms, population, etc). Am I right about this?

Now some specific questions, (page numbers are from the 2nd edition of the boo).

Pag 65: the three new categories created are simply an exercise, they are never used later on nor added to the data set. Right or false?

What are the hyperparameter? What is the score (mentioned in section "Select and train model"). It is also mentioned the model is overfitting the data but i dont understand why.

Pag 72: the code from this page is also never used?

Thanks for your help