The bottom bar is called the command line. As already mentioned, it functions as text input bar. Anything you type using your keyboard will appear down here. To send a message to your primary frequency hit the primary frequency send key you defined in you [[General Settings]] and not [ENTER]. To send text messages or give in commands use [ENTER] (further details under [[Working with keyboard]])
The right side of this bar is an info bar. Clicking on screen items e.g.: aircraft, controller, ATIS, etc. you can get detailed information. On the left side, the callsign of the currently selected aircraft is displayed. You can clear the content of the command edit and if it already edit deselect the aircraft with the [ESC] key.