Loot tables are technical JSON files that represent what items should be in naturally generated containers, what items should drop when breaking a block or killing a mob, or what items can be fished. It does not affect dropped experience, or dropped non-item entities such as slimes from larger slimes or silverfish from infested blocks. Official Minecraft Wiki
Creating a Loot table
- Click on "Add New Mod Element"
- Choose "Loot table" and name it.
- Set the properties of the loot table
- Save your mod element
Loot table properties
Registry name: Click on the dropdown list and choose the "category" of the loot table. It doesn't define the loot table type. It's only to standardize loot table names. After, you have to change the last part of the name (after the "/") for your name. For example, I'm making a new loot table for the cow. I will select "entity/chicken" and replace the "chicken" by "cow".
Namespace: If you want to change a vanilla loot table, you have to choose "minecraft", but if you want to create a new loot table for your mod, choose "mod".
Type: It will define which type of loot table you make.
Loot table pools
Loot table pool: A loot table pool is a group of blocks/items or a single block/item. When the game has to use the loot table, it will take a random number of blocks/items of each pool (between the minimum and maximum you have set). You can put as many pools as you want in one loot table.
Min rolls: It's the minimum number of blocks/items the game will take. (You can put it to 0.)
Max rolls: It's the maximal number of blocks/items the game will take.
Bonus roll(s): The bonus rolls are an optional option used to add a possibility to give more rolls to a specific pool. (The min and max work the same way than before).
Entry item: The block/item
Entry weight: It's the maximum possible number of the block/item you have chosen.
Add loot table pool: Add a new pool in the loot table.
Remove this pool: Remove this whole pool
Add pool's table entry: Add a new entry in the pool
Remove this entry: Remove this specific entry
If you prefer to watch the video, you can find the wiki page above summarized in a video: