RStudio rownames_to_column - How to find name of first column to use in this function?

Oh! So, first columns never have names? You have to assign them?

In the mtcars example, why would someone want to create major, defining column that identifies each unique observation, like make/model, and leave the column name blank?

Another example was the hotel_booking sample data set. I couldn't find a reservation_ID column.
I don't get it...
Thanks!