my ibook appear horizontal but l want it vertical

Depending on what you are reading your books on, if you are reading on a iPad Pro 12.3.1 (that's what I have ) - swipe down from the very right hand top of the page. Controls will appear , in the left side column there is a "lock" with a circular arrow around it. Tap on that. it locks and unlocks your auto-rotation ability. With it off, you should be able to turn your iPad vertically or horizontally to read. So if you want to keep everything vertical, lock it when it is in that position.