Most of this info is covered in the Getting Started, be sure to follow them as best as you can.
When you first run TShock, it will inform you of an Auth-Code in the console. You may log in to the server and use this code to verify your character as the super admin. This will also lock the auth code system. You must join the server on your character, use /auth [authcode] and then register and log in. Then use the /auth-verify command. To register and log in you need to run the command /register [password] to create an account under your username with the password you put in. Now you may use /login [password] to login. You must use the password you used upon registration.
TShock Upgrades to UUID
An interesting aspect about TShock as of Terraria 1.2 is that TShock may now use your UUID to log you in! This means that if you are using the same computer and same character as you did when you registered then you will be automatically logged in upon joining the server.
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