ACTIVATING/DEACTIVATING THE WHITE LIST
In order to activate/deactivate the white list, you must first login to your Clanforge panel. Once in, select edit profile>Config>Server.properties.  In there, you can enable or disable the whitelist. Make sure to restart your server after saving the settings on that page.
Alternatively, with some versions of Minecraft, you can also run these commands from the console to control white listing:
whitelist on
whitelist off

ADDING USERS TO THE WHITE LIST (File: whitelist.json)

IMPORTANT: Before you can add a user to the whitelist, make sure to first allow that user to join your server with the whitelist off so that the server "knows" their UUID/username. Once that is done, you will then be able to re-enable whitelisting and add them as described below.

You can also add a user via console or in the game itself. To edit via console, you will need to click on "console" in the game panel under the navigation menu. You can add users to the white list by typing into the console the following: whitelist add username
To add the user in-game, you would follow the same format: /whitelist add username
This method does not require a restart.

EXAMPLE SYNTAX / FORMAT FOR THE WHITELIST
white-list.txt
notch
user1
player2

whitelist.json
[
  {
    "uuid": "uuid-goes-here",
    "name": "notch"
  },
  {
    "uuid": "uuid-goes-here",
    "name": "user1"
  },  {
    "uuid": "uuid-goes-here",
    "name": "player1"
  }
]

* UUIDs can be found via Clanforge>Edit Profile>Config>User Cache if the player has already joined the server.