Make yourself operator and use a whitelist

Type these commands in the panel Console, without a / in front. Replace YourName with the exact Minecraft username.

Become operator (admin)

op YourName

Remove it again with deop YourName. Only give op to people you fully trust; they can run every command.

Turn on the whitelist

whitelist on
whitelist add YourName
whitelist add FriendName

Now only people on the list can join. Useful commands:

• whitelist list: see who is on it
• whitelist remove Name: remove someone
• whitelist off: let everyone join again

Using ranks? A permissions plugin like LuckPerms is safer than giving people op.