Character select is to be able to switch to another character on the account without need to exit the game and reconnect (you have to create the other character first). But i think the default maximum character on an account is 1. You will have to take a look in the config.json in the server folder (..\Server\resources\config.json). Take a look at line 14 ("MaxCharacters": X,) if the number is 1 then set it to the number that you want.
Else if you only want one character per account than i think that you can disable the button on the ui folder in the client folder.