Getting the token
To be able to register as an admin on your Terraria server, you need your unique token. This token is generated when you start the server for the first time, then you open the live console where you can find the token:
In this case the token is 4914096.
Enter the token in game
In order to be able to register as an admin, join your server in Terraria and enter the command /setup 4914096 in the game. Of course you replace the token 4914096 with your own.
The following message will then appear in the chat:
Adding an Admin
Now you can add a new admin to your server with the command /user add USERNAME PASSWORD owner. You replace USERNAME with your name and as PASSWORD you can choose any password you like which you can use in the future to login as admin on your server.
Note that your password must be at least 4 characters long!
Login as Admin
After you have registered in the game as admin, you can log in with the following command: /login USERNAME PASSWORD
Of course you replace USERNAME with your name and PASSWORD with the password you set before.
Now you are logged in as admin on your server and can manage it with different commands.