The text of a standard novel is read one page at a time — in sequence, from first page to the last. Gamebook text, however, is broken into sections that don't read in sequence. Instead, each paragraph (or chapter, in some cases) ends in a choice with a corresponding page number — that the reader must turn to
in order to view consequences of that choice.
By adding these choices, reading becomes more interactive. Different paths can be followed with different consequences — sometimes assuaging that page-counting feeling of hopelessness experienced by many neophyte readers when faced with The Complete Works of Hazlitt
Yet, our initial claim can't be overstated: nobody sells good reading habits. Feel free to say that gamebooks are an outdated, pop-culture attempt at diverting attention in that direction. The beginning reader still needs to want to read.