The wires you added to the breadboard it easy to connect circuits you build on the terminal stips to supply voltages on the bus strips.  

The two levels of supply voltage in your prototyping system are 3 V and 0 V. 

You can connect a circuit to 3 V by plugging a wire or lead into one of the center and right bus strips’ plus (+) sockets.  Those are the ones next to the red lines, and also shaded red in the animation. 

The other supply voltage level on the breadboard is 0 V, which is also called ‘ground’ and abbreviated GND.  The 0 V level is available from all three bus strips’ minus (-) sockets.  Those are the ones next to the blue lines, and also shaded blue in the animation below.  

(View full size: bb-voltage-zones.mp4)