Shields
Shields are used in combat to defend yourself in the fight against evil. Shield schemes are first introduced as a quest reward after crafting your first dagger--in turn, receiving the a wooden shield scheme . The first shield is a little more difficult to acquire than the dagger because it requires leather--a material found as early as the third floor of the Dungeon. However, once you have overcame this hurdle, further shields can be either found or crafted after complete their respective schemes.
Shields and their schemes are dropped from various monsters found throughout you adventures. After obtaining a new shield, whether same or different tier, they can be equipped alongside of your weapon in the backpack's second tab labeled Gear Items. This tab has unlimited inventory space, in theory, but will become laggy after collecting so much. In order to prevent this from happening too often, gear can be dropped to free space; however, this is not recommended. It is recommended to wait until the LOD quest, in which you will be able to disassemble. Additionally, when new gear enters your inventory, it will be auto-sorted by the date it was received and denoted by an exclamation mark (!) until viewed by either a long tap (hold item icon for brief preview until finger is lifted) or short tap (opens preview but needs secondary tap to close).
Shields can be placed in the fourth slot in the player GUI section of the Currencies & Minerals tab or equipped in the same manner as tools: tap the icon and select equip. Once equipped, you will be unable to unequip it. Instead, you will have to collect another shield and swap it for the existing one.