From the introduction:
Welcome to this third volume in the Riddles series. The previous entries have proved quite popular so we thought we'd wade in with yet more riddles for a more modern age. We thought this time that we'd focus on more modern riddles with this volume rather than an all round generic theme, although many of the presented puzzles can quite easily be used for virtually any genre of play.
To use this publication you can either randomly roll a D100 to allocate a riddle, or simply choose directly which riddles you want to use! Yes, it's really that simple.
Of course, I'd like to point you in the direction of the first two Riddles titles, available from the same place you purchased this book. not only will they give you more riddling options, and no doubt amuse for hours!