The idea
A recipe, not a one-off tidy-up
Cleaning a spreadsheet by hand works once. Next month's file arrives and you do it all again.
Power Query records what you did as a list of steps. Point it at the new file and the same clean-up replays in a second, in the same order, with no chance of doing it slightly differently.
That list is the whole idea of this chapter. Everything else is which steps exist.
Check against your class slides. No Power BI material exists in the export, so this chapter is reconstructed from the outline's topic wording and the textbook.