Downward force of magnitude 5 N is exerted on the book by the force of gravity. We call that the "weight" of the book.
At the same time, upward force of 5 N is exerted on the book by the table. This one is called the "normal force".
Since the vertical forces on the book are 'balanced' (add up to zero), the book just lays there on the table, and does not accelerate.
