Whitelisting can be very important for your Minecraft server. If you enable whitelist you can choose who can join your Minecraft server, you can add the players you want to your server, anyone not added will not be able to join your server. If you just want to play survival with friends and don’t want anyone else to login and grief your base it is very smart to enable a whitelist. 
Enabling and adding people to a whitelist requires that you are either an OP, have permissions in a different way, or you have access to the console. (To Give yourself op type the following in the console: “op (playername)” or see our guide how to manage permissions on your minecraft server. 

How to enable whitelists
To enable whitelists type “/whitelist” in game if you have operator permissions, or type “Whitelist” in the console if you have access To turn it off again type “/whitelist off” or “Whitelist” in the console

How to add or remove players from the whitelist
Type /whitelist add (name) or whitelist add (name) in the console. To remove people type /whitelist remove (name) or whitelist remove (name)
Additionally you can type /whitelist list to see who is whitelisted. Or on the server hosting panel if you go to your files folder you can find the whitelist.json file and see an overview of the UUID of all whitelisted players and the username