Tome is an implement group. The normal tome costs 7 gp and weighs 1 pound. Using a tome by itself confers no benefit, but you can purchase an enchanted implement to gain an enhancement bonus or use a class feature to gain such a benefit.
An arcanist wizard gets a special ability with the Tome of Binding class feature. Once per encounter, as a free action, if you use your tome when using an arcane summoning power, all creatures summoned by that power gain a bonus to damage rolls equal to your Constitution modifier. You must wield a tome to benefit from this feature.[AP:98]