Click the Select a window button, which is the second button to the left in this panel, to add a window to be recorded. Select the desired window by hovering the mouse over the area until the window has focus, click left mouse button to return to the main interface. Debut will capture the image from this window and will keep focus on it even if it is moved or resized during recording.
Note: On Windows 8 or 10 the Selection Tools will not be displayed when in Tablet mode, because of how Windows manages the windows on tablet mode.