These options control what pressing the Tab does in Listers.
Tab:
Cycle through all Lister user interface elements: Pressing the Tab will move the focus from one element to the next. When you reach the final element the focus will loop back to the first one.
Switch source/destination in dual-display Listers: If the Lister is in dual display mode then the Tab key simply switches the source and destination states of the two displays; it doesn't move the focus to any other element.
Ctrl+Tab:
Display popup tab switcher: Pressing Ctrl+Tab will activate the popup tab switcher.
Switch source/destination in dual-display Listers: In dual display mode, pressing Ctrl+Tab switches the source and destination states of the two displays.
Ctrl+Shift+Tab:
Display popup tab switcher: Pressing Ctrl+Shift+Tab will activate the popup tab switcher.
Switch source/destination in dual-display Listers: In dual display mode, pressing Ctrl+Shift+Tab switches the source and destination states of the two displays.
No action: Nothing happens when you press Ctrl+Shift+Tab.