Melee weapon attacks use strength to attack and cause wounds. Ranged weapon attacks use dexterity to attack and cause wounds, but throwing weapons use dexterity to attack and strength to cause wounds. Using a weapon in a way other than its intended purpose, or using an improvised weapon, gives disadvantage on attack and damage rolls.
Some attacks and the wounds they cause ignore armor and cannot be avoided using a shield, such as mind-affecting spells, poison gas, siege weaponry, or fire.
Depending on the genre and setting, enhanced weapons and armor could take the form of prototype science fiction technology to magical fantasy armaments. While this equipment is better than normal items, it never manifests in numerical bonuses or advantage on dice rolls. Instead, enhanced weapons and armor provides new abilities, like a suit of sealed power armor that can also function as an EVA suit or an enchanted sword that can harm undead who are immune to normal weapons. A good rule of thumb to follow is this: If an enhanced weapon or armor would only give a small numerical bonus on rolls using it, it doesn't need to be an enhanced item.