You can use the command in-game /whitelist on to enable the whitelist which will only give users you grant access to the ability to join the server. To add a player to this list, use /whitelist add username. If you are entering this command on the Live Console use whitelist on and whitelist add username instead.
Also, be sure to check the Settings tab to ensure that the whitelist option is enabled.
If you would like your server to not appear on our public community server list, you can set it to Not Visible from your dashboard.
Please let me know if you have any other questions.