For general data pack information you can look here and here.

ActionInventory mod uses data packs to locate what inventories and openers to load.
Data packs have the following structure:

(data pack name)
  ├ pack.mcmeta
  ├ pack.png
  └ data
    └ (namespace)
      └ actioninventory
        ├ inventories
        | └ (inventory).json
        └ openers
          └ (opener).json

The (data pack name) and (namespace) can be anything you want. The inventories folder holds the files for all inventories and the openers folder holds the files for all openers.

You have to put the data packs into the datapacks folder for each world. If you want data packs to automatically be added to all worlds you can use a mod like Data Loader.

Example Pack.zip
(pack_format may need to be changed depending on Minecraft version)