Whitelisting a minecraft server is simple and it prevents any unauthorized entry to your own server. This is prefered to be in use, if your server has sable playerbase, your kids, group of friends etc. Whitelisting works with minecraft nickname what is connected to spesific UUID.
ACTIVATING/DEACTIVATING THE WHITE LIST
In order to activate/deactivate the white list, you must first login to your game panel. Once in, click on "Files", then navigate through "Config" to "Server Settings". In there, you can enable or disable the whitelist. Make sure to restart your server after saving the settings on that page.
You can now 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. But if you are in game it requires you to be OP'd.