Double window lets you take the best out of the screen allowing you to access two terminal windows at the same time. To activate it just click on the Double Window icon on the tools menu.
The first time you click in the Double Window icon, it will divide the screen into two horizontal windows, a second click will divide the screen into two vertical windows, a third click will take you the single screen again.
When you execute a command its result will be shown in the active window. To work on the other window or change the active window, just click on the window you wish to work on.