Armor
Armor is an important way to stay alive when fighting Monsters. Armor increases your Maximum HP, which helps you stay alive longer in many situations.
Armor is made of metal, and you will need to provide some ore as part of the cost to purchase the upgrade. The deeper you go in the mine, the better ore you will find and you can use it to forge better armor.
Armor is best used in conjunction with a Helmet.
Many of the more difficult Monsters will kill you in a few hits if you don't have decent armor. Armor is also a must-have to defeat the bosses you might find later in the game, so be sure you upgrade it as much as you can!
You can also augment your armor with certain items to make it stronger and give it extra abilities. There is no limit to how many times you can augment your armor, and you keep the augments even if you upgrade your armor again.
Just don't forget to buy a big enough meal at the Tavern to heal back up after you've taken damage.