I don't understand the "Hold" mechanic. (I have a physical copy of the book, so if it has been updated in the PDF, please let me know.)
The book basically just says it is a resource that can be generated and spent, but doesn't really say HOW to gain or spend it.
Thank you for picking up a physical copy and reaching out! Hold is generated by moves that generate Hold as part of their effects, and Hold is spent to use that move's specific effects. For example, the Basic Move get some answers generates Hold when a hit is rolled, and this hold is spent to ask one of that move's questions. You can think of moves that use Hold as having "charges" that can be spent at a later point during a scene. Hold only applies in the context of Hold-using moves, so don't worry about it unless a move says you should.