Like all +2 weapons, the DM will add +2 to the AC hit when using this weapon but the damage bonus has already been factored into the damage wheel.
When attacking a Giant with this weapon, if a natural 20 is slid and the 10 in the ✸ is closest to the damage dot on the combat board, the Giant will be slain.
When attacking non-Giants, this is an “ordinary” +2 weapon.