Question

A book is sitting on a desk. What best describes the normal force acting on the book?

Answer 1

This image describes it better than I can type it: http://hyperphysics.phy-astr.gsu.edu/hbase/imgmec/normal.gif
Also this website, hyperphysics, is pretty helpful in general.

Answer 2

The book has mass, so gravity is accelerating it toward the centre of the earth.
But the book is not moving — the table is holding it up with a normal force the opposes the gravitational force exactly.