Ancient Debris is the name of the second rarest ore in the game called Minecraft, added in 1.16 for Minecraft Java Edition and Minecraft Bedrock Edition. Found exclusively in The Nether between y levels 8 to 22, this one is considered as the only legitimate source of Netherite Scrap.
This ore floats on lava in item form, cannot be burned, and has the same blast resistance as obsidian but is able to be moved by pistons. Ancient Debris is able to be used for smelting to create Netherite scraps, which is able to be used to create netherite ingots. This one is the first thing that you have to find on the adventure to the Netherite and as stated before, you have to find it in the Nether. When you go through the Nether portal, please dig down to find it. It is because the chance of finding it is higher depending on how many blocks above the bottom of the world you are.
The sad news is that because the Nether portal is able to be generated at any random level in the Nether, it is not possible to say how far you have to dig down. You have to know your starting position and you can do it by pressing F3. It will show you a ton of debug information but on the left hand side of the screen will be three coordinates: X, Y, and Z. While all three are important to remember for your Nether portal location, please pay attention to the Y-axis in order to increase the chance of finding Ancient Debris.
The Y-axis will tell you how many blocks you are above the bottom layer of the whole world. Ancient Debris is able to spawn in veins 1-3 blocks at Y-axis 8-22 and it is able to spawn in veins of 1-2 blocks at Y-axis 8-119. The sentence means the maximum number of Ancient Debris blocks you can find in one chunk (64×64 block section of the world) is five.
Aside from that, the Ancient Debris is also able to only spawn completely covered by either blocks or lava, meaning you will have to start a Nether mineshaft and you will not run into any while sauntering across the Nether surface.
After you have got the Ancient Debris, you can start smelting it in a furnace with any fuel source. An Ancient Debris will produce a Netherite Scrap and unluckily, you have four Netherite Scrap if you want to make one Netherite Ingot. In addition, you also need four Gold Ingots if you want to make one Netherite Ingot, as you combine them with the four Netherite Scrap. It means getting enough Netherite Ingots for a full kit will take a while. Keep in mind that the placement of the scrap and ingots in the crafting grid does not matter, as it is a shapeless recipe. Once you have created some Netherite Ingots, you are able to start crafting both tools and armor.