How do I make myself (and then someone else) a server admin?

After installing the TS3 server, you will be shown a Server Admin Token ID either on screen (Windows) or you can also find it from your logs in the log directory. Once you have this, copy it and launch the TS3 client and connect to your server as a normal user. Now, go to Permissions > Use Token and paste the Token ID into the box. If successful, this will make you a Server Admin and you should see a "SA" icon next to your name.

Note the token can only be used ONCE. After you're logged in as a Server Admin you can create a new token for someone else to use by going to Permissions > Token Manager > Add Token and choosing Server Group for type and Server Admin for group then clicking Create. You can then email or provide the token to another user allowing them to do the same thing.