I think the numbers you're referring to are the
xx/yy numbers. Those numbers refer to the condition of the weapon/armor.
xx part refers to the current condition of the item, which degrades with usage. Weapons degrade when they're used to attack and armor degrades when you receive damage from enemies. When an item's condition reaches 0 and it is used, it'll break and lose all its effectiveness. You'll either have to repair it at a blacksmith or use a repair kit.
yy part refers to the maximum durability of the item.