All messages in this channel will be displayed in the Game Window right above the character's head. All characters who are visible on the game window will be able to read your statements. It is also possible to raise or lower your voice being able to whisper and yell (see it here and here). When you say a spell it will always appear in this channnel. Clear the messages from the console window by repeatedly pressing Ctrl+W (Tibia 10) or Alt+W (Tibia 11's default hotkey).
See also:Channels, Chat Commands, and Console