Buckets are tools used to carry water, lava, milk, powder snow, live fish and axolotls. If the empty bucket is part of a stack and the player's inventory is full, the filled bucket drops in front of the player as an item.
Empty buckets in Minecraft can be used to pick up a water or lava source block by pressing the use item on a block of the relevant type. Similarly one can press use when looking at a cow, goat to fill a bucket with milk. Empty buckets can also be used to collect fish in buckets.
To make a bucket, you will need:
The recipe requires three iron ingots. You will need at least a stone pickaxe to mine iron ore.
View How to make a bucket in Minecraft for more details.