For those familiar with Carbuncle 1.0 (possibly nobody), it was a basic chat room and server hosting tool. Well now in version 2, it's the same thing, but not really.
Basically version 2 is a server lobby -- so it lists Terraria servers that are being hosted at the remote location -- and also a chat room with basic functions.
To register, all it takes is a unique username and a password of up to six characters, and no more. (A short password is forced to prevent complex passwords that you might use for other services. In other words, it's just a security measure.) If the username is truly unique, then the account will be registered, and all it takes to log in again is the same combination (yes it's case-sensitive).
Hosting (and how it works)
Hosting Terraria servers is up to the service host--whoever is running the remote server software. (There are no downloads to your PC or network in the form of files from the server software. Inversely, world files can be uploaded to the remote host to be run in configuration with your requested Terraria server.) Basically, input the requested information in the form, or rather user interface that is built into this program, and then after the server starts, you will be whispered the TShock admin code in the chat room.