Chains are metallic decorative blocks that can be found in mineshafts, bastion remnant chests, and on the ceiling in bastion remnants. They were added to the game in the ‘Nether Update’ in v1.16.
Chains being hung from the ceiling (via screenshot)
You can either craft chains, can pick up naturally generated ones, or find them in loot chests. For crafting them, you will need an iron ingot and two iron nuggets. By placing them in a vertical formation with the iron ingot at the center and the nuggets on the top and bottom, you will be able to craft a chain.
Crafting a chain (via screenshot)
To pick up naturally generated chains found in bastion remnants and mineshafts, you will need to use a pickaxe as they will drop nothing if broken with a different tool. In bastion remnants, chains will always generate above magma cube spawners and sometimes inside ruined portals. For mineshafts, you will find naturally generated chains on the sides of wooden bridges. These chains are generated vertically in a pillar between the ceiling and the bridge. You can also find them in loot chests scattered across mineshafts and bastion remnants.
A lantern hung from the ceiling of a bastion remnant (via screenshot)
Chains are decorative blocks and are used as such. They are commonly used to suspend bells and lanterns from ceilings. The texture of the chain and the lanterns (both normal and soul lanterns) connect with each other seamlessly as if they were made for each other. Chains do not need a supporting block to be hanged from and can exist completely free-standing in mid-air. You can also rotate them horizontally.
Using chains to suspend lanterns (via screenshot)
Chains are a great decorative block that are most commonly used to suspend lanterns. Since you can walk on them and they can be rotated horizontally, you can make expensive but inconspicuous bridges.
A. Yes, you can walk on chains but it requires precision.
A. You will need to place one iron ingot and two iron nuggets in a straight vertical line in the crafting grid.
A. The most common place to find chains is in bastion remnants.