Where are Page Up and Page Down on a Mac?

Full-size Apple keyboards and any PC keyboard have Page Up and Page Down keys, and they do what you expect: scroll a screen at a time without moving the cursor. MacBooks leave them out; there, fn↑ is Page Up and fn↓ Page Down.

The habit worth picking up: in Safari, Chrome, Preview and most readers, Space pages down and ⇧Space pages up, no fn needed.

To move the cursor a page at a time while editing text, ⌥Page Up and ⌥Page Down (with fn on a MacBook) in TextEdit, Pages and Xcode; Word and Excel use the plain keys the way they do on Windows.

Home and End are the other pair that moves, and they scroll to the top and bottom of the document rather than to the line ends; see Where are Home and End.