The ways they are used are subject to social pressures, that may well be different for boys and girls. I would then expect that the fundamental features of imaginative activity will be common, and that relatively superficial differences will be caused by different socialization, and perhaps there is also a genetic factor of indeterminate influence. This engages newly literate students, I argue, because it tells in detail about the extremes of reality and the limits of experience. In my informal surveys, boys slightly prefer the book to girls. Both sexes find it engaging on the whole, but there are differences, even if slight, whose cause may be to do with the way the book is aimed preferentially at a male audience, the kinds of 'records' that are given the main focus, etc. etc.
Imagination is the ability to think flexibly and effectively about the possible.
That is the subject of the first chapter of the book. I'm not sure I can add much to it. The first part of this question is what I address in Chapter 2 of the book. Again, I can't think of much to add. And the second part of the question is what most of the rest of the book addresses.