Open the loot_tables folder in the plugin directory. Make a new file called somename.yml.

Edit the file with your favorite text editor (preferably not notepad).

Here are some samples of what you could put in the file:

apples:
  id: APPLE
  chance: .5
  rolls: 4
  amount: 3
a_sword:
  id: IRON_SWORD
  chance: .3
  rolls: 1

In game, target a chest and type /cr set loot_table somename.yml.

This will tell the chest to restock with: 1-4 apples 1 iron sword