Leather

Leather can be acquired by killing cows. When killed, cows will drop 0-2 pieces of leather.

Leather is used to craft the lowest tier of armor. 24 pieces are required to craft the full set: Though it doesn't make very durable armor, it is the easiest of armor materials (leather, iron,chainmail(By Hacking),gold or diamond) to obtain in the beginning of a new save and can help surviving the first few nights.
 * 5 pieces for the cap
 * 8 pieces for the tunic
 * 7 pieces for the pants
 * 4 pieces for the boots

Trivia

 * Leather armor used to be crafted with Wool.
 * Leather is the least durable armor, but this is balanced by the fact that it is the only renewable armor set in the game.

Leder