A user login name and password like in TeamSpeak 2 do no longer exist. Instead TeamSpeak 3 uses a public/private key mechanism where each user is assigned a unique identifier. This is your "key" to the server and all permissions are bound to this unique identifier. The private key is stored on your computer and not shown anywhere in the client. This private key must be kept secret. The public key, shown in many places in the client, can be given to other users to identify yourself. If you lose your private key, your user account is lost and cannot be recovered. If anyone is asking you for your private key, he is trying to cheat you.
Source - TS3 FAQ