Clay Ball

Clay is the item obtained from diging clay blocks, which are usually found in diamond-shaped groups in shallow water, and are best dug using a shovel. Each block yields four clay balls. Clay deposits are most easily found in the water in swamp biomes, but also appear in rivers, and abundant deposits are to be found in oceans, though you might want some enchanted gear or an underwater base to excavate it. You can harvest hardened clay and clay blocks in mesa biomes if you plan on using the clay for making bricks.

Usage
Clay can be crafted back together to form clay blocks or baked in a furnace to create bricks. Bricks can then be crafted into a block or into flower pots. Clay blocks can be heated in a furnace to make hardened clay, however this is wasteful because mesas, although rare, reward the player with literal mountains of the stuff. It can then be dyed with various dyes to create colored blocks that are not flammable like wool is.