Items make up all equipment and creatures such as bows and humans.
There are five diffrent kinds of items
First off Creatures are the first item you pick when creating a unit and can be Humans to Demons some creatures such as Catapults will take away all four other slots which means no Weapons, Shields, Armor and Specials on that creature.
Second Weapons, weapons can be Daggers to Bows and Staffs to War hammers.
Third is Shields, shields add defense but some weapons such as Spears and Muskets block the usage of shields.
Fourth is Armor armor greatly increases your defense and some have resistances for example +5 ice resistance.
And Finally Specials specials can either be mounts or accessories such as a wizard ring.