After clicking "Start" on the launcher window and entering your account ID and password, you will arrive at the world selection screen. A character can only exist on the world in which it is created, and cannot interact with characters from other worlds. So if you have friends already playing Knight Online, make sure to find out in which world their characters reside. Also, each world has 2 sub-servers from which to choose. All sub-servers are part of the same world, and hence will retain your character information as you move from one to the next. To log in, click on the server name, then click on one of the three sub-servers, and finally click "Connect".