This guide will help you to understand on how to become an administrator and how to use commands while on the server.
Start your server and join it.
Once connected, press [F2] key to open player list.
Locate your player name on the list and copy the player ID.
Stop your server.
Navigate to your File Manager → worlds and edit the adminlist.txt
Start your server and join it, press [F5] key to open console and type “help” for all available commands.
Commands can be used in the console.