Before version 1.9, your "offhand" didn’t exist. You held a sword in your right hand and maybe a bow in your left. The Combat Update added a dedicated (press 'F' by default).
: An "off-hand" slot was added, allowing you to hold a second item (like a torch, shield, or map) while using your main weapon. Pressing F quickly swaps items between hands. version 1.9 minecraft