You can add signals using the Add Menu or the Ctrl key shortcuts.
Digital Clock - Add Menu -> Clock - Ctrl 1
Digital Signal - Add Menu -> Signal - Ctrl 2
Digital Bus - Add Menu -> Bus - Ctrl 3
The signal panel is displayed on the left of the timing diagram. After entering all the paramenters, hit the “Add” Button. This new signal will appear in the timing diagram below the last signal. You can position the signal in the diagram, moving it up to the preferred position.